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A convenient procedure is proposed for extracting mitochondrial proteolipids using a single phase mixture chloroform-methanol-water (1:2:0.8 v/v) with subsequent separation of the phases. The proteolipids were concentrated at the interface between the phases and thus purified from the bulk of the phospholipids. It was found that the mitochondrial proteolipids represent stable complexes of phospholipids with some low molecular weight proteins (M(r) = 7-18 kDa). The latter are destroyed at acid pH values. The phospholipid/protein ratio was found to be equal to 6 (assuming the molecular masses of the proteins and phospholipids to be equal to 10 and 0.8 kDa, respectively). The phospholipid composition of the tightly bound proteolipids thus obtained did not differ from that of the mitochondrial phospholipids. Using 31P-NMR, nonbilayer structures were found to arise from proteolipid reconstitution into multibilayer liposomes.

The lipid and proteolipid composition of endoplasmic reticulum smooth membranes from rat enterocytes in normalcy and under D-hypovitaminosis is studied to show the Ca2+-binding with these components. These membranes in vitamin D-deficiency are established to differ in the cholesterol content. Proteolipids 1 and 2 are isolated from the lipid fraction of membranes. Their amino acid composition is determined. The vitamin D-dependent binding of Ca by the proteolipid fraction is shown.

Artificial membranes were reconstructed from differently purified proteolipids (PL) of cattle brain white matter. The related lipids had different quantitative (72, 50-45 and 15-8%) and qualitative content. Conductance of the artificial membranes of all three types of PL in 0.1 M solutions of alkaline metal chlorides were 2-3 orders above that of bilayer membrane of lecithin and brain phospholipids. In all the cases the PL membranes with 85-92% protein content had the highest conductance, and those with 28% protein content--the lowest. Introduction of liposomes of PL and lecithin mixture to one side of the bilayer lecithin membrane brought about a gradual increase of its conductance up to a definite high level. The membranes made of all three types have specific conductance to monovalent cations which are arranged in the following order: Na+ greater than K+ greater than Cs+ greater than Li+.

The Folch-Lees proteolipid complexes of different purity (crude proteolipids and relative pure proteolipids) were isolated from vertebrate brain: mammalia (Macaca irus, Macaca rhesus and white rat), birds (Columbia livia), reptilia (Testudo horsfieldi), amphibia (Rana temporaria) and fishes (Salmo irideus). The proteolipid complexes were isolated by emulsion-centrifugation method. The content of proteolipid protein (mg/g w. w.) correlates with the level of phylogenetic development of the animals studied. It is the highest in monkey brain (10.5 and 8.6 mg/g) and the lowest in fish brain (2.2 mg/g). The yield of proteolipids from the brains of animals studied shows the same pattern. Crude proteolipids of mammalia, birds and reptiles contain 40-50% of protein and 60-50% of lipids. The content of phospholipids is about 40%. Proteolipids of amphibia and fish brain contain less protein--about 30%. In the conditions of mild purification, the protein content in mammalia, birds and reptilia makes up about 70% and lipid content--about 30-35%. The crude and purified proteolipids in all the animals studied (as compared with the original lipid extracts from which they were isolated) are enriched in acid phospholipids: phosphatidyl serine, phosphatidyl inositol and diphosphatidyl glycerol. Acid phospholipids in total lipid extract make up 10-20% of total phospholipids, in crude proteolipids 16-32 and in purified proteolipids--56-75%. There are no marked differences between fatty acid composition of phospholipids in proteolipids and in the same phospholipids isolated from total lipid extract.

Proteolipid complex of Folch-Lees has been obtained and purified from the myelin and synaptosomes of the brain of the frog Rana temporaria and hen Gallus domesticus. Relative content of this proteolipid and glycolipids in the myelin is almost twice higher, whereas that of phospholipids--1 1/2 times lower than in the synaptosomal membranes of the same animal. Protein content of this complex is higher for myelin than for synaptosomal membranes; opposite relation was found with respect to phospholipid content. Within this complex, lipids are presented mainly by phospholipids, especially by acid ones which amount to 30-60%. Proteolipid complexes fro the myelin and synaptosomes differ from each other by their lipid component. Myelin proteolipid complex contains mainly phosphatidylserine and phosphatid acid, whereas synaptosomal one--phosphatidylserine and diphosphatediglycerol. No significant differences were found in fatty acid composition of phospholipids from proteolipid complex from myelin and synaptosomes as compared to this composition in the initial membranes.

From the whole brain of animals representing 5 classes of vertebrates--mammals (Macaca rhesus and albino rat), birds (the pigeon Columba livia), reptiles (the tortoise Testudo horsfieldi), amphibians (the frog Rana temporaria) and fishes (the trout Salmo irideus), as well as from myelin preparations of mammals (dog, rabbit and rat) proteolipids have been isolated by emulsion--centrifugation method. It was shown that extraction procedure results in the loss and destruction of several proteolipid complexes. In all the animals investigated, the main loss (from 25 to 75% of all complexes) was observed during emulsion--centrifugation stage, especially during 10-min centrifugation at 200 g. During extraction of proteolipids from the whole brain, under the conditions employed, the lost proteolipids are presumably those which belong to the myelin fraction. To prevent excessive proteolipid loss, the final low speed centrifugation step should be avoided. It was shown that in order to obtain proteolipids in a soluble form in a mixture of chloroform and methanol, total proteolipids from the brain of mammals should contain not less than 27% of phospholipids. Studies were also made on the composition and relative content of phospholipids in proteolipids extracted from the whole mammalian brain and myelin preparations. With respect to phospholipid composition, proteolipids from the whole brain significantly differ from those obtained from myelin fraction. Myelin fraction, being itself rich in proteolipids, contain large amounts of phosphatidyl serine (up to 69); however, proteolipids of this fraction contain lower amounts (4%) of diphosphatidyl glycerol as compared to proteolipids from the whole brain (22%).(ABSTRACT TRUNCATED AT 250 WORDS)