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In the apple variety 'Usterapfel', there are two known genotypes, which differ in malic acid content. One hundred days after full bloom, low-acid fruit (LA-fruit) contained 125 micromolg(-1) dry matter (DW) of malate, while the high-acid genotype (HA-fruit) reached levels up to 627 micromolg(-1) DW. There was no difference in the catalytic activity of enzymes involved in malate metabolism, such as PEPcarboxylase, malate dehydrogenase, and NADP malic enzyme. After [14C]glucose incorporation into the excised tissue of either genotype, the organic acid fraction was labeled to approximately the same extent. Furthermore, uptake of [14C]malate was significantly lower in excised tissue of LA-fruit. These findings suggest that low malate content in LA-fruit is the result of a restricted ability to accumulate malate in apple parenchyma cells. The different ability to accumulate malate had a pronounced effect on overall carbon partitioning. However, the rate of respiration and the rate of malate synthesis was similar in both genotypes. In HA-fruit, the glycolytic flux through pyruvate kinase was increased to compensate for the carbon that accumulated in the vacuole as malate. Since malate storage in the LA-fruit was restricted, it was more easily available for gluconeogenesis, and was correlated with a three-times higher activity of PEPcarboxykinase. LA-fruit showed higher concentrations of ATP, which stimulated Glc6P and fructose-6-phosphate formation. The elevated hexosephosphate content led to an enhanced partitioning of carbon into starch (+40%), hemicellulose (+104%), and sucrose (+40%) in more mature fruit. The activation of carbohydrate synthesis resulted in a significant drop in glucose-1-phosphate (Glc1P). To meet the increased demand for Glc1P, the activities of neutral and acid invertase, hexokinase, and phosphoglucomutase were higher in LA-fruit. Glucose was a more versatile substrate for this metabolic route than was fructose. It was also evident that glycolytic flux in apple was dependent on glucose level, and that the reaction catalysed by phosphoglucomutase contributed to the regulation of carbon partitioning between malate and carbohydrate polymers.

The red pigment uroerythrin, a chromophore known to be adsorbed by the amorphous urate sediments (sedimentum lateritium), has been isolated from human urine and further purified as its trimethyl derivative. Urine was applied to a column of Amberlite XAD-2 resin on which uroerythrin and other pigments were adsorbed. The pigments were eluted with methanol and uroerythrin was further purified by extraction with ether at pH 4.0, repeated chromatography on lipophilic Sephadex LH-20 and thin-layer chromatography on silica gel. For optimal purification uroerythrin was converted into the trimethyl derivative and chromatographed on silical gel thin-layer plates. The structure of the pigment has been studied by chromate degradation followed by identification of the imide products by thin-layer chromatography. From these results and from infrared, mass spectral and nuclear magnetic resonance data a tripyrrole structure for uroerythrin is concluded. The proposed structure for the chromophore is related to that of the bile pigment biliverdin consisting, however, only of the rings A, B and C.

Besides the synthesis of urea, ammonia detoxication at high concentrations can also be effected through enzyme reactions involved in glutamic acid metabolism. These mechanisms are also operative in extrahepatic tissues. Hyperammonemia is also found in the animal model of the portacaval shunt (PCS) rat. This model was chosen to study the activities of glutamate dehydrogenase, glutamine synthetase and glutaminase I in liver, brain and kidney 10, 20 and 30 days after PCS. In brain and kidney ammonia is detoxified mainly by the glutamate dehydrogenase and glutamine synthetase reactions whereas in the liver these enzyme reactions play a minor role.

At high systemic blood concentrations ammonia may be partially deviated into the pathway of pyrimidine synthesis, as has been observed in different genetic defects of the urea cycle. The portacaval shunt (PCS) rat presents an animal model to study ammonia detoxication without an underlying enzyme defect in the urea cycle. Since ammonia may induce a deviation into the pyrimidine pathway by influencing enzymatic reactions involved in this pathway, the activity of carbamylphosphate synthetase and aspartate transcarbamylase in liver as well as the excretion of orotic acid in the urine were measured in rats 10, 20 and 30 days after PCS. The results suggest that in this experimental model ammonia may be channeled into the pyrimidine pathway leading to a stimulation of the first enzymatic step and to an increased excretion of orotic acid.

A reliable and practicable method for the determination of short chain fatty acids in plasma and brain tissue is presented. The sample preparation by partition chromatography on silicic acid allows subsequently a quantitation of short chain fatty acids without interference by methylmalonic acid, or other more polar compounds. With the gas-chromatographic system 2-methylbutyrate is separated from isovalerate. Reference values are given for plasma. The system is also useful in combination with mass spectrometry.

Arginase was isolated from human liver and erythrocytes. The purification procedure used acetone precipitation, heat-treatment, (NH4)2SO4 precipitation, DEAE-cellulose chromatography and gel filtration on Sephadex G-200 in the presence of 2-mercaptoethanol. Both enzymes migrated to the anode at pH8.3 on polyacrylamide-gel electrophoresis. After incubation at pH8.0 and 37 degrees C the purified anionic liver arginase migrated to the cathode on polyacrylamide-gel electrophoresis. It is assumed that the multiple forms of the enzyme reported in the literature are partly artifacts of the purification procedure. The liver arginase showed a mol.wt. of 107000 determined by gel filtration and a sedimentation coefficient of 5.9S. Treatment of the liver enzyme with 0.25% sodium dodecyl sulphate at pH10 demonstrated an oligomeric structure of the enzyme with a mol.wt. of the subunit of 35000. The kinetic properties determined for the purified liver arginase showed an optimum pH of 9.3 and an optimal MnCl2 concentration of 2mM. The Km for L-arginine was 10.5 mM and for L-canavanine 50mM, and L-lysine exhibited a competitive type of inhibition with a Ki of 4.4mM. L-Homoarginine was not a substrate for liver arginase.