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This is the first report of the effect of prostaglandins on the biochemical pathways for fatty acid synthesis. PGE2 and PGF2α inhibited fatty acid elongation in a lung microsomal fraction. Neither prostaglandin affected the de novo, or soluble, system for fatty acid synthesis (i.e. acetyl CoA carboxylase or fatty acid synthetase). The results also suggest that the initial inhibition of fatty acid synthesis leads to a decrease in free fatty acids available for esterification into phospholipids. The site and possible mechanisms of inhibition are discussed.

Extract: Fatty acids are important components of pulmonary surface-active lipids and lung membranes. We have investigated fatty acid synthesis in developing rabbit lung by measuring the rate of incorporation of (14C)acetyl or (14C)malonyl-CoA into pentane-extractable fatty acids. Because the lung can incorporate exogenously supplied as well as endogenously synthesized fatty acid into phospholipid, parallel studies of hepatic fatty acid synthesis were carried out. Fatty acids can be synthesized in fetal rabbit lung by the de novo pathway and to a lesser extent by chain elongation. The activity of enzymes related to de novo fatty acid synthesis is at adult levels by 23 days of fetal life and remains fairly constant thereafter. Enzymes associated with hepatic de novo fatty acid synthesis reach very ‘high levels of activity during fetal life but this decreases by 50% after birth, in association with the onset of suckling. Activity of the enzymes of de novo pulmonary synthesis appears to be unaffected by birth and onset of nutritional intake. Pulmonary and hepatic fatty acid elongation do not appear to be major routes of fatty acid synthesis in the fetal rabbit. Microsomal elongation activity is low in the fetus and on the first day of life, adult activity being fourfold greater. Pulmonary mitochondrial elongation becomes progressively more active during fetal life, but quantitatively appears less important than de novo synthesis. Gas-liquid chromatography of the fatty acids synthesized by fatty acid synthetase in the supernatant fraction of lung homogenates revealed that the main product was palmitic acid, a major component of dipalmityl lecithin which is an important surface-active lipid. The maior products of pulmonary mitochondrial and microsomal fatty acid elongation were stearic acid and 20− and 22-carbon unsaturated fatty acids. The early maturation of the enzymes of the de novo pathway ensures a source of fatty acid for lung membrane growth and for surfactant formation when the pathways for lecithin synthesis mature. Speculation: Inasmuch as the enzymes associated with de novo fatty acid synthesis are active before the pathway for lecithin synthesis matures, fatty acid synthesis is probably not the rate-limiting factor in surfactant production in the rabbit fetus. The role of other lecithin precursors such as choline remains to be investigated. Early dietary intake does not appear to influence pulmonary fatty acid synthesis, but may play an important role in overall pulmonary lipid metabolism and the regulation of lung surface activity.

We have characterized two mutants of Escherichia coli in which fatty acid biosynthesis is adversely affected by elevated temperature. Under conditions which do not alter the activity of wild type cell-free extracts, virtually all of the malonyl coenzyme A-acyl carrier protein (ACP) transacylase and fatty acid synthetase activities present in mutant extracts are thermolabile. Malonyl transacylase from wild type cells restores normal fatty acid synthetase activity to inactivated mutant extracts. Furthermore, fatty acid synthesis in mutant extracts is corrected by malonyl-ACP. Malonyl transacylase and fatty acid synthetase activities are also restored in revertants which were selected for their ability to grow at elevated temperatures. These experiments furnish evidence that the mutants are altered in the structural gene for malonyl transacylase and that this is their only genetic defect. When these strains, defective in the synthesis of a substrate vital for fatty acid elongation, are grown at elevated temperatures, their phospholipids become deficient in long chain acyl groups. Supplementation of these cultures with long chain fatty acids permits sustained growth and the maintenance of a normal fatty acid composition.

The structure and composition of the cutin monomers from the flower petals of Vicia faba were determined by hydrogenolysis (LiAlH4) or deuterolysis (LiAlD4) followed by thin layer chromatography and combined gas-liquid chromatography and mass spectrometry. The major components were 10, 16-dihydroxyhexadecanoic acid (79.8%), 9, 16-dihydroxyhexadecanoic acid (4.2%), 16-hydroxyhexadecanoic acid (4.2%), 18-hydroxyoctadecanoic acid (1.6%), and hexadecanoic acid (2.4%). These results show that flower petal cutin is very similar to leaf cutin of V. faba. Developing petals readily incorporated exogenous [1-14C]palmitic acid into cutin. Direct conversion of the exogeneous acid into 16-hydroxyhexadecanoic acid, 10, 16-dihydroxy-, and 9, 16-dihydroxyhexadecanoic acid was demonstrated by radio gas-liquid chromatography of their chemical degradation products. About 1% of the exogenous [1-14C]palmitic acid was incorporated into C27, C29, and C31n-alkanes, which were identified by combined gas-liquid chromatography and mass spectrometry as the major components of the hydrocarbons of V. faba flowers. The radioactivity distribution among these three alkanes (C27, 15%; C29, 48%; C31, 38%) was similar to the per cent composition of the alkanes (C27, 12%; C29, 43%; C31, 44%). [1-14C]Stearic acid was also incorporated into C27, C29, and C31n-alkanes in good yield (3%). Trichloroacetate, which has been postulated to be an inhibitor of fatty acid elongation, inhibited the conversion of [1-14C]stearic acid to alkanes, and the inhibition was greatest for the longer alkanes. Developing flower petals also incorporated exogenous C28, C30, and C32 acids into alkanes in 0.5% to 5% yields. [G-3H]n-octacosanoic acid (C28) was incorporated into C27, C29, and C31n-alkanes. [G-3H]n-triacontanoic acid (C30) was incorporated mainly into C29 and C31 alkanes, whereas [9, 10, 11-3H]n-dotriacontanoic acid (C32) was converted mainly to C31 alkane. Trichloroacetate inhibited the conversion of the exogenous acids into alkanes with carbon chains longer than the exogenous acid, and at the same time increased the amount of the direct decarboxylation product formed. These results clearly demonstrate direct decarboxylation as well as elongation and decarboxylation of exogenous fatty acids, and thus constitute the most direct evidence thus far obtained for an elongation-decarboxylation mechanism for the biosynthesis of alkanes.

Sphingogalactolipids (galactocerebrosides and sulfatides) have been isolated in almost quantitative yields from normal human nervous tissue (mostly brain) at different ages and their fatty acid compositions have been determined by gas-liquid chromatography. The ratio of hydroxy acids to normal acids increased slightly during myelination and then remained rather constant; in adults the ratio for cerebrosides was about 2, and for sulfatides, 0.6-0.8. In adult nervous tissue the two predominant fatty acids of cerebrosides and sulfatides were the C(24) monounsaturated and 2-hydroxy saturated acids. The infant brain galactolipids had (compared with child and adult) a lower percentage of C(22)-C(26) fatty acids and a much lower percentage of monoenoic acids, both of normal and hydroxy acids. Low activities of fatty acid elongation and desaturation systems during myelination are inferred. Fatty acid changes with age were the same for cerebrosides and sulfatides but occurred later in the sulfatides, which supports the hypothesis that the cerebrosides are precursors of the sulfatides. The adult pattern of fatty acid composition with regard to degree of unsaturation and total percentage of C(22)-C(26) acids was reached as early as at 2 yr of age, but the percentage of odd-numbered (C(23) and C(25)) fatty acids continued to increase up to the age of 10-15 yr. The fatty acid composition of the galactolipids of peripheral nerves differed mainly in its lower percentages of C(25) and C(26) acids and higher percentages of C(22) and C(16) acids. This composition is thus intermediate between those of brain and of extraneural organs.

1. 1. Dietary aflatoxin reduced the incorporation of acetate-14C into long-chain fatty acids of chick liver (Gallus domesticus) in a dose-related fashion. 2. 2. Feeding 10 μg of aflatoxin per g of diet for 3 weeks depressed the activities of the microsomal system of fatty acid elongation and fatty acid synthetase in liver. 3. 3. Crystalline aflatoxin did not inhibit fatty acid synthetase in vitro at levels up to 20 μg/ml of incubation medium. 4. 4. It is suggested that aflatoxin exerts its effects on lipogenesis by depressing the formation of the enzymes involved in fatty acid synthesis.

Submitochondrial particles prepared from rat liver mitochondria or Triton extracts of these particles incorporate 1-14C-acetyl coenzyme A into fatty acids in the presence of ATP and reduced pyridine nucleotides. Added acyl-CoA primers can substitute for ATP. NADPH is 25% as active as NADH, and its activity is not explicable on the basis of its conversion to NADH. It appears that NADPH may also be a direct reductant in the elongation reaction. It was shown that ATP supports acetyl-CoA incorporation by activating endogenous fatty acids via an acyl-CoA synthetasecatalyzed reaction. Gas-liquid chromatographic separation of the products and analysis of the amount of radioactivity present in the carboxyl carbon of the synthesized fatty acids were consistent with the operation of a chain elongation mechanism. The fatty acid products of the reaction were identified as CoA esters, 2 to 4 carbon atoms longer than the primer fatty acyl-CoA. The elongation reaction was found to occur in both the inner and outer mitochondrial membranes as well as in the soluble fraction. The inner membrane and the soluble fraction were highly active with decanoyl-CoA and octanoyl-CoA but exhibited almost no activity with long chain acyl-CoAs. On the other hand, the specific activity of the outer membrane preparation with palmitoyl-CoA was three times higher than that found in the inner membrane. The elongation reaction was inhibited by oxidized nucleotides, CoA—SH, and acyl-CoAs. The incorporation of 2-14C-malonyl-CoA was considerably lower than that of acetyl-CoA and could be accounted for by the presence of a highly active malonyl-CoA decarboxylase in the preparations. Both the acyl-CoA deacylase and the malonyl-CoA decarboxylase appeared to be localized in the matrix fraction of rat liver mitochondria.

Elongation of palmityl-CoA to longer chain fatty acids by the high molecular weight fatty acid synthetase from Mycobacterium phlei requires a factor present in boiled mycobacterial extracts in addition to and distinct from the polysaccharides (3 - O - methylmannose - containing polysaccharide (MMP) or lipopolysaccharide that contains 6-O-methylglucose and glucose (MGLP)) which support the de novo synthesis of fatty acids from acetyl-CoA in this system. This elongation factor (EF) has been purified 46-fold and is shown to be a protein with a molecular weight of about 10,500. EF catalyzes the hydrolysis of long chain acyl-CoA derivatives and the following evidence indicates that it functions as a thioesterase in palmityl-CoA elongation. (a) Elongation and thioesterase activities show parallel chain-length specificities for acyl thioesters from C10 to C18. (b) The two activities are inactivated at similar rates on heating at 50°. (c) Elongation and thioesterase activities migrate the same distance on gel electrophoresis at pH 8.5. (d) Thioesterase I from Escherichia coli can replace EF in stimulating palmityl-CoA elongation by the Mycobacterium phlei fatty acid synthetase. (e) Free coenzyme A, in adequate concentrations, stimulates palmityl-CoA elongation as effectively as EF. It is concluded that EF, by virtue of its thioesterase activity, adjusts intracellular concentrations of palmityl-CoA and free CoA to levels which are favorable for chain elongation. The regulatory significance of thioesterase activities is discussed.

The malate-aspartate, fatty acid, and α-glycerophosphate shuttles for the transport of reducing equivalents into mitochondria were reconstituted, using isolated hepatic mitochondria and the extramitochondrial components of the shuttles. Clofibrate and thyroxin increased, while propylthiouracil treatment decreased, the activity of mitochondrial α-glycerophosphate dehydrogenase. Despite these changes, the activity of the reconstituted α-glycerophosphate shuttle was similar in mitochondria from control rats and those from rats treated with clofibrate and propylthiouracil. There was an increase in the activity of the shuttle using mitochondria from thyroxin-treated rats. Rotenone caused 60–90% inhibition of this shuttle, suggesting that rotenone-sensitive NADH dehydrogenase participates in the pathway of oxidation of extramitochondrial hydrogen. Palmitate, oleate, and octanoate were equally effective in reconstituting a cyclic fatty acid shuttle. The shuttle was inhibited by various compounds affecting mitochondrial metabolism, including oligomycin, dinitrophenol, cyanide, rotenone, atractyloside, and α-bromopalmitate. Carnitine and several dicarboxylic and tricarboxylic acids which stimulate fatty acid elongation, augmented fatty acid shuttle activity. The malate-aspartate shuttle was inhibited by cycloserine, amino-oxyacetic acid, and hydrazine, and stimulated by pyridoxal phosphate, at the same concentrations which affected the activities of cytoplasmic and mitochondrial glutamic oxalacetic transaminase. This shuttle was inhibited by uncouplers, antimycin, azide, cyanide, rotenone, amobarbital, oligomycin, and several inhibitors of anion transport including iodobenzylmalonate and avenaciolide. The reconstituted shuttle is sufficiently active to provide about 70–80% of the oxalacetate required for maximal rates of gluconeogenesis. Extrapolations based on the rates of mitochondrial oxidation of acetaldehyde and the activity of the microsomal ethanol oxidizing system suggest that any one of the shuttles could account for the rate of ethanol metabolism in vitro by the alcohol dehydrogenase pathway.

Beef heart mitochondria contain at least two membranes: an inner membrane with infoldings (cristae) of a tubular nature, and with distinctive tripartite subunits; and an outer membrane with repeating subunits of a different nature and size. The inner membrane, which can be isolated in a relatively pure form, contains the four complexes of the electron transfer chain as well as enzymes such as ATPase. The outer membrane, which has also been isolated in a relatively pure fraction, contains the ancillary mitochondrial enzyme systems that implement citric acid cycle oxidation, fatty acid oxidation, fatty acid elongation, and substrate level phosphorylation. The outer membrane can be isolated either as a composite fraction (F) or in two distinct and separate fractions, one a particulate membranous fraction (K), and the other a soluble nonmenbranous fraction (S). In the present series of three communications we have described the preparation and properties of the soluble membrane fraction (S), the particulate membrane fraction (K), and the composite outer membrane fraction (F). The S fraction contains the citric acid cycle enzymes of low molecular weight, e.g., isocitric dehydrogenase, malic dehydrogenase, condensing enzyme, fumarase, and aconitase. This fraction also contains significant amounts of the enzymes concerned in oxidation and elongation of fatty acids as well as of enzymes with transfer function such as myokinase. The S fraction has been designated as the detachable sector of the outer membrane.

The incorporation and metabolic alteration of a variety of dietary fatty acids has been studied in wild-type Saccharomyces cerevisiae and a fatty-acid auxotroph which carries a genetic defect in its fatty-acid synthetase complex. This mutant grows when supplemented with a singleven or odd chain-length fatty acid ranging from 13–17 carbon atoms. Although incapable of fattyacid synthesis from acetate de novo, the mutant yeast still elongates the dietary fatty acids by one or more C2 units. The extent of elongation is dependent on the chain length of the fatty acid included in the growth medium. It is most evident with tridecanoic acid and insignificant with palmitic acid. All saturated fatty acids are desaturated to an appreciable but varying degree to the corresponding monounsaturated acids. No degradation to lower homologues is observed in the wild-type, nor in the mutant cells. No evidence was obtained to indicate participation of the mutant fatty-acid synthetase complex in the elongation process described. In wild-type yeast, intracellular fatty acid biosynthesis is unimpaired by the addition of free fatty acids to the growth medium and apparently proceeds by a much faster rate than the uptake and elongation of fatty acids from the growth medium. A membrane-bound enzyme analogous to acid : CoA ligase has been isolated from bakers' yeast and its chain-length specificity studied. The optimal chain length with saturated fatty acids is 15 carbon atoms. Unsaturated fatty acids are generally better substrates. The role of fatty acid activation in determining the rate of fatty-acid-dependent yeastmutant growth is discussed.

— Quantitative analyses of white matter from four brains of patients with multiple sclerosis (MS) and four control brains were carried out for total and soluble proteins, individual lipid fractions, and their corresponding fatty acids. In three specimens from two of the MS brains there were reductions of cerebrosides and of the C20:1 acid in the ethanolamine glycerophosphatide (EGP) fraction and a slight increase of tetraenes and trienes, while all other components were present in concentrations similar to those in the controls. In three other samples from two of the MS brains, galactolipids were deficient to a greater extent than cholesterol, EGP or CGP (choline glycerophosphatide), while proteins were within the control range. In samples where thinning of myelin was observed in Luxol-blue stained sections, there were proportional decreases of all components. The percentage of C20:1 acid in the EGP fraction was reduced in two of three myelin preparations from corresponding samples of MS white matter, and that of C24:1 acid in the cerebroside fraction was reduced in all three MS myelin preparations when compared with the two controls. The data suggest that inadequacy of the fatty acid elongation process together with deficits of cerebrosides represent one of the early biochemical lesions in the white matter of the MS brain.

Chronic ethanol feeding to rats leads to an increased rate of ethanol metabolism. This increase is not accompanied by altered permeability of the mitochondria to NADH. The activities of the reconstituted malate-aspartate, fatty acid elongation and α-glycerophosphate shuttles for the transport of reducing equivalents into mitochondria were not changed by chronic ethanol ingestion. Thus, in contrast to other reports, these results show that neither increased mitochondrial permeability nor enhanced shuttle activity explains the acceleration of ethanol metabolism produced by chronic ethanol ingestion.

We have investigated fatty acid synthesis by the developing heart. The only system for fatty acid synthesis in the heart is the mitochondrial elongation pathway. Myocardial fatty acid elongation was very low prenatally but increased rapidly during the first week of life. Coincident with weaning there was a sharp drop in elongation activity possibly related to a shift from the high fat intake provided by the milk to the carbohydrate diet provided by standard laboratory chow. Either NADH or NADPH could provide reducing equivalents for myocardial fatty acid elongation. The presence of a long-chain fatty acid primer in the medium resulted in a higher incorporation of acetyl-CoA throughout the developmental period. However, the ratio of endogenous fatty acid elongation activity to that in the presence of an added primer increased with age presumably in relation to the postnatal increase in the availability of long-chain fatty acid primers. Products of fatty acid elongation in postnatal rats included a range of saturated and unsaturated fatty acids with major peaks of stearic acid (18:0) and 20- and 22-carbon unsaturated fatty acids suggesting elongation of the palmityl-CoA primer by the-two carbon units of acetyl-CoA. Decarboxylation of fatty acid products indicated that all synthesis could be accounted for by chain elongation. The observed developmental changes in myocardial fatty acid elongation may be related to functional, structural, and nutritional adaptations of the cell to the postnatal environment.

Incorporation of fatty acids of chain length C 2 to C 14 into the C 16 acid of Brassica oleracea was not inhibited by trichloroacetate at concentrations sufficient to inhibit their incorporation into paraffins almost completely. The sensitivity to trichloroacetate of incorporation of fatty acids into paraffins remained nearly the same when the chain length of the precursor fatty acid was increased from C 2 to C 16 , but incorporation of C 18 acid into paraffin was much less sensitive to trichloroacetate. Carbons 1 and 2 of stearic acid were incorporated into nonacosane at the same rate as the entire C 18 molecule, showing that C 18 acid does not undergo degradation of its carbon chain before being incorporated into the paraffin. These results support the hypothesis that the C 16 chain is elongated to a C 30 unit which on decarboxylation gives rise to the paraffin. Light and 3-(4-chlorophenyl)-1,1-dimethylurea (CMU) affect incorporation of C 18 into neither paraffins nor very long fatty acids; trichloroacetate inhibits C 18 incorporation into paraffins and to a lesser degree into very long fatty acids, suggesting that the formation of such acids is related to paraffin synthesis. The time course of incorporation of C 18 acid into very long fatty acids and paraffins failed to show a precursor-product relationship, and the very long fatty acids were found to be esterified in the phospholipids and triglycerides of the particulate structures. On the basis of present knowledge it is proposed that C 16 acid becomes the substrate for an elongation-decarboxylation enzyme complex which is situated somewhere outside the chloroplasts. This enzyme complex elongates C 16 to C 30 , decarboxylates this C 30 unit, and releases the paraffin from the complex. During the elongation process dissociation of small amounts of fatty acids occurs at each stage. These are rapidly estfieried into phospholipids and triglycerides.

The objectives of this study were to identify the subcellular fraction responsible for fatty acid synthesis in rabbit aorta and to determine the effect of cholesterol feeding on the system. A method for homogenization of aorta is described which permitted the isolation of subcellular components of aorta, including mitochondria that were morphologically and functionally intact. Mitochondria were identified as the major site of fatty acid synthesis in this tissue. Cofactor requirements and products showed that the synthetic system operates by chain elongation. Mitochondria from atherosclerotic aortas incorporated acetate into fatty acids faster than did mitochondria from control aortas. It is concluded that cholesterol feeding leads to alterations of aortic mitochondrial function and accelerates the fatty acid elongation pathway.

Oxidation, synthesis, and desaturation of fatty acids were assessed in chick embryos and embryonic liver. No differences in the oxidation of palmitate-1-14C and oleate-1-14C by intact embryos and embryo-liver homogenates were found. De novo fatty acid synthesis and microsomal elongation of fatty acids were detected in embryo-liver homogenates, but the activities were low as compared with chick liver. The specific activities of the mitochondrial system of fatty acid elongation were similar in embryo and chick liver. Stimulation of the desaturation of stearic acid was achieved by the substitution of glucose for fatty acids in the culture medium and abolished by the addition of cyclopropene fatty acids to the medium. The hypothesis is advanced that in chick embryos, the rate of desaturation of fatty acids synthesized de novo is less than that of postembryonic liver, and that as a consequence, the liver of embryos cannot maintain the proportion of unsaturated to saturated fatty acids found in yolk.

The characteristics patterns and asymmetric distribution of phospholipid fatty acids suggest precise control mechanisms. Our investigations were designed to assess mitochondrial fatty acid elongation and their pattern of incorporation into complex lipids. Fatty acid chain elongation in the total lipid fraction occurred primarily with the more abundant fatty acids present. Elongation patterns in free fatty acids were similar to the total lipid fraction except C20:4 and C22:4 were formed to slightly greater extent. Choline glycerophosphatide and ethanolamine glycerophosphatide displayed different patterns of elongation. Choline glycerophosphatide contained more elongated longer chain polyunsaturated fatty acids, while ethanolamine glycerophosphatide contained greater amounts of elongated shorter chain saturated and monounsaturated fatty acids. These results suggest that fatty acid elongation may play a specific role in fulfilling mitochondrial phospholipid fatty acid requirements.

— We have studied the fatty acid compositions of cerebral myelin lipids in phenyl-alanine-treated and control rats. The proportion of long chain fatty acids and the ratio of unsaturated to saturated fatty acids of whole brain lipids was low in the penylalanine-treated animals. Both of these reductions were more pronounced in the myelin from phenylalanine-treated rats. The ratio of unsaturated to saturated fatty acids in ethanolamine phosphatides was markedly decreased in the hyperphenylalaninemic condition. The reduction in the proportion of long chain fatty acids was predominant in non-hydroxy fatty acids in cerebrosides and ethanolamine phosphatides. The lipid composition of the myelin expressed as mole percentages of individual phospholipid and sphingolipid components was not significantly different in the two groups of rats, nor did it change with age. Our results indicate a deficiency in the fatty acid elongation and desaturation system in the brains of phenylalanine-treated rats. We suggest that in hyperphenylalaninemic rats, a reduction in the amounts of unsaturated fatty acid and long chain fatty acid alters, respectively, the biochemical reactivity and the stability of the myelin.

We have investigated interactions of palmityl-CoA and l -palmitylcarnitine as substrates for mitochondrial fatty acid elongation. l -Palmitylcarnitine is a more effective substrate primer for fatty acid elongation by intact mitochondria than is palmityl-CoA. Exogenous l -carnitine inhibited l -palmitylcarnitine-supported mitochondrial fatty acid elongation by both sonically disrupted and intact heart mitochondria, probably by shifting the equilibrium between palmitylcarnitine and palmityl-CoA toward palmitylcarnitine, thus removing palmityl-CoA from the reaction. d -Carnitine was without effect. d -Palmitylcarnitine inhibition of palmitylcarnitine transferase activity decreased palmitylcarnitine-stimulated mitochondrial fatty acid elongation but increased palmityl-CoA supported fatty acid elongation, presumably by increasing the effective concentration of palmityl-CoA in the assay medium. The data indicate that, although l -palmitylcarnitine is an effective substrate primer for mitochondrial fatty acid elongation, palmityl-CoA rather than palmitylcarnitine is the immediate precursor for fatty acid chain elongation.

In homogenates of chick-embryo liver and in the subcellular fractions isolated from those homogenates the mitochondrial system of fatty acid elongation and fatty acid synthetase can be measured independently. The assay medium for measuring the microsomal system of fatty acid elongation also measures some mitochondrial elongation activity. Acetyl-CoA carboxylase (acetyl-CoA: carbon dioxide ligase (ADP), EC 6.4.1.2) can be measured independently in the cytosol but not in the crude homogenates, presumably because of the activity of the mitochondrial enzymes pyruvate carboxylase (pyruvate: carbon dioxide ligase (ADP), EC 6.4.1.1) and propionyl-CoA carboxylase (propionyl-CoA: carbon dioxide ligase (ADP), EC 6.4.1.3). 1. 2. The predominant system of fatty acid synthesis in chick-embryo liver is mitochondrial elongation ; microsomal elongation and fatty acid synthetase activities are low in comparison. 2. 3. The activities of fatty acid synthetase and acetyl-CoA carboxylase in livers of 15-day embryos can be stimulated by injection of 180 mg of glucose into eggs at 4.5 days of incubation.

1. 1. A RSACA technique has been developed and found useful in the study of the amount of contribution of fatty acid elongation vs. de novo synthesis. 2. 2. The limitations of this technique were determined by the use of authentic chemically and enzymically prepared fatty acids with 14 C in different positions. 3. 3. Hydrogenation prior to Schmidt degration was determined to be essential for samples rich in unsaturated fatty acids. 4. 4. Tables were calculated for interpretation of data obtained by this RSACA technique, taking into consideration the size of the precursors and length of the final fatty acids.

The fatty acid shuttle for the transport of reducing equivalents into mitochondria was reconstituted in vitro . Externally added citrate increased the activity of this shuttle 30–40%. Citrate also stimulated the activity in the absence of added fatty acid (endogenous rate). The effect of citrate was prevented neither by inhibition of citric acid cycle activity nor by blocking citrate transport into the mitochondria. Inhibition of citrate efflux from the mitochondria impaired shuttle activity. A fatty acid elongation system in the outer membrane, which is stimulated by citrate, may be rate-limiting for the fatty acid shuttle.

Biochemical changes signaling irreversible damage in brain cells following hypoxia are incompletely understood. Disruption of membrane structure may play a role in this process. Lipids and long-chain fatty acids are important constituents of neural membranes and could serve as markers of membrane breakdown. The present study was undertaken to assess the brain lipid profile and the process of fatty acid elongation in adult rats subjected to hypoxia and unilateral carotid ligation. Following functional recovery from hypoxia, the brain lipids were analyzed in both hemispheres and disclosed a significant reduction of inositide glycerophosphatide (PI) and serine glycerophosphatide (PS). Mitochondrial fatty acid elongation was increased by more than 100% and the pattern of elongation more closely resembled that seen during myelination rather than maturity. Although the degree of brain hypoxia is not predictable in the rat model, the lipid alterations indicate a reparative process following a suppression of lipid metabolism during hypoxia. Delineation of biochemical processes signaling irreversible brain damage will await further studies on regional and subcellular changes.

The “Quaking” mouse is a mutant which has an inherited disease involving the process of myelination in the central nervous system. Fractionation of brain lipids and fatty acid methyl ester analysis of each lipid isolated have been performed. No qualitative abnormalities have been detected, either in ethanolamine, serine and choline phosphoglycerides, or in cholesterol. Proof has now been obtained that the considerable reduction in long chain fatty acids (C24), occurs in cerebrosides, sulphatides (where they are normally major constituents) and in sphingomyelin. Long chain hydroxylated fatty acids are comparatively less diminished than non-hydroxylated one. This metabolic defect, detected in all the sphingolipids that contain this type of fatty acids could be in favour of a mutation related to fatty acid elongation which is very important at the time of myelin formation.

A comparative study was made on the fate of linoleic, arachidonic, and docosa-7,10,13,16-tetraenoic acids in various subcellular fractions of liver and testis from rats of different ages. It was demonstrated that testicular microsomes can desaturate and elongate linoleic and arachidonic acids in a manner similar to liver microsomes, and that testicular mitochondria can convert docosa-7,10,13,16-tetraenoic acid to arachidonic acid. Testicular or liver microsomes actively desaturate linoleic acid to γ-linolenic acid and eicosa-8,11,14-trienoic acid to arachidonic acid. However, it was impossible to measure in vitro any direct conversion of adrenic acid (22:4 [n – 6]) to docosapentaenoic acid (22: 5 [n – 6]) by either liver or testicular microsomes. Docosa-7,10,13,16-tetraenoic acid is incorporated preferentially into the triglyceride fraction of total testis, mitochondria, and microsomes, while linoleic and arachidonic acids are incorporated more into phospholipids. The capacity of testicular microsomes, but not of liver microsomes, to synthesize polyunsaturated fatty acids declines with age. It is proposed that the synthesis of acids of the linoleic family proceeds in two stages, a rapid one in which arachidonic acid is made and a second, slower, one in which C22 and C24 acids are synthesized. In addition, there appears to be a cycle between microsomes and mitochondria that acts to conserve essential polyunsaturated C20 and C22 fatty acids by means of synthesis and partial degradation, respectively. This cycle would restrict the loss of essential fatty acids and might be of importance for the supply of arachidonic acid in testis under specific requirements and especially in older animals., Facultad de Ciencias Médicas

ELONGATED fatty acids in the brain are of interest because they are thought to contribute to membrane stability and cohesiveness1,2. Using a technique similar to that described by Aeberhard and Menkes3, the developmental pattern of fatty acid elongation was assessed in the rat brain4.