Biomedical subjects
Publications and source records attributed to L D Bergel'son.
Neutral glycosphingolipids of murine T-lymphoma EL-4 were studied. The major glycolipid components were identified as GlcCer, LacCer, GgOse3Cer and GgOse4Cer. It has been shown for the first time that not only gangliosides but also neutral glycolipids are shed from the cell surface into the outer medium.
The binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, a platelet activating factor (PAF), to plasma components was studied. Gel filtration and lipoprotein fractionation revealed the presence in the plasma of PAF-binding fractions corresponding to plasma albumin as well as of low and high density lipoproteins. Incubation of PAF-containing lipoproteins with rabbit platelets resulted in a transfer of PAF to the platelets. PAF bound to plasma albumin is less exchangeable than PAF bound to lipoproteins. The PAF-transferring efficiency of high density lipoproteins (HDL) and of low density lipoproteins (LDL) correlates with the amounts of HDL- and LDL-receptors on the platelet surface. It may thus be assumed that PAF released by various cells interacts with lipoproteins which further transport the bound PAF to target cells carrying lipoprotein receptors.
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The phage T7 DNA complexes with various phospholipids (PL) were studied by 31P NMR at PL/nucleotide molar ratio of 2 : 1. Using a phosphatidylcholine thion analogue, the contributions of PL and DNA into the 31P NMR spectrum of the complex were estimated. It was found that PL-DNA interaction results in partial immobilizing ability of PL depends on their structure, increasing in the following row: phosphatidylcholine-phosphatidylethanolamine less than sphingomyelin less than or equal to ternary mixture of these PL. The data obtained are indicative of nonequivalent binding of DNA with various PL species.
The binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, a platelet activating factor (PAF), to individual classes of human plasma lipoproteins was studied. It was found that PAF is rapidly incorporated into plasma lipoproteins. The degree of PAF binding to the lipoproteins depends on their type. Analysis of PAF binding in Scatchard plots revealed that HDL2 contain high affinity binding sites for PAF. On the other hand, LDL bind PAF in a nonspecific manner. Incubation of PAF with human plasma results in inhibition of lecithin: cholesterol acyltransferase (LCAT)-catalyzed cholesterol esterification. On the contrary, prostaglandin E1 stimulates LCAT activity in human plasma. PAF and prostaglandin E1 do not compete with each other for the binding sites in HDL2. It is concluded that incorporation of PAF into plasma lipoproteins may influence the LCAT activity in vivo.
The effects of exogenous glycosphingolipids on the cytotoxic activity of natural killer (NK) cells and on the sensitivity of target cells were studied. Incubation of splenocytes with gangliosides of the hemato-series (GM3 and GD3) or with their precursor, LacCer, decreases the cytotoxic NK-activity, whereas some other acidic and neutral glycolipids do not possess such capability. On the other hand, incubation of target (YAC lymphoma) cells with glycolipids of the hemato-series increases the sensitivity of these cells to the cytotoxic action of NK-cells. A comparison of the ganglioside profiles of two YAC call lines differing in their NK-sensitivity revealed the presence of a GD3-like component in the highly sensitive cell line and the absence of this ganglioside in low sensitive target cells. It is assumed that gangliosides of the hemato-series are components of the acceptor complex on the surface of the target cells and that shedding of these gangliosides (especially, of GD3) by tumour cells is one possible mechanism of NK-activity suppression during malignant growth.
The effects of the phospholipid composition of rat liver microsomes on the differential binding spectra of cytochrome P-450 with type I and II substrates (hexobarbital and aniline) were studied. Lysophosphatidylcholine was found to decrease the binding of both type substrates. These changes were reversible, and the spectra were restored by exchanging the microsomal lysophosphatidylcholine for unsaturated phosphatidylcholines, but not with dipalmitoylglycerophosphocholine, sphingomyelin, phosphatidylserine, and phosphatidylethanolamine. Phosphatidylinositol favoured only the binding of type II substrates. The data obtained indicate that the substrate binding capacity of cytochrome P-450 depends specifically on the "boundary" lipids, but not on the bulk lipids of the microsomal membrane.
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Synthesis of fluorescently labeled cerebrosides--N-[12-(9-anthryl)-11-trans-dodecenoyl]-1 beta-O-galactosylsphingosine and its 9-(3-perylenoyl)nonanoyl analog is described. Both probes are easily inserted in phosphatidylcholine vesicles.
A comparative study of gangliosides from bovine normal lymph lymphocytes and leukemic blood lymphocytes and from calf thymocytes incubated at different cell densities was carried out. The ganglioside composition of thymocytes and normal lymphocytes was insensitive to the variations in cell density. In the case of leukemic lymphocytes the decrease of cell density resulted in a reduction of the absolute and relative content of one of the major ganglioside components, disialosyllactosylceramide, and in a concomitant increase of its precursor, N-glycoloylneuraminosyllactosylceramide. The content of the third major ganglioside component, sialosylparagloboside, did not depend on cell density. The cell density dependent changes in the ganglioside composition of leukemic lymphocytes are qualitatively coincident with those observed at variable concentrations of blood lymphocytes in leukemic animals. A possible mechanism underlying the differences in ganglioside metabolism during cell density changes in leukemic lymphocytes is discussed.
The ganglioside composition of thymuses from pigs of different age, of embryonal human thymus and of thymus from newborns was studied. Pig thymus was found to contain 8 ganglioside fractions, i. e. N-acetyl- and N-glycoloylneuraminosyllactosylceramides (GM3), N-acetyl- and N-glycoloylneuraminosylgangliotetraosylceramides (GM1), (N-acetylneuraminosyl, N-glycoloylneuraminosyl)- and di(N-glycoloylneuraminosyl)lactosylceramides (GD3), N-glycoloylneuraminosylgangliotriaosylceramide (GM2) and a fucoganglioside. The ganglioside spectrum of pig thymus did not change with ageing. In embryonal human thymus and in thymus of newborns four ganglioside fractions were determined, i.e. GM3, N-acetylneuraminosylneolactotetraosylceramide GM2 and GD3. A comparison of the experimental results with literature data suggests that ganglioside GD3 is a marker of immature lymphoid cells displaying a marked phylogenetic stability.
The lipid dependence of the pyrophosphatase activity of microsomes from rat liver and hepatoma was studied. Two methods were used for modification of the lipid composition of the microsomes: delipidation with organic solvents followed by relipidation with phospholipid vesicles and transformation of the microsomal lipid composition by lipid exchange proteins. In contrast to glucose 6-phosphatase, microsomal pyrophosphatase activity was found to be insensitive to modification of the membrane lipid composition by the above method. Possible causes of the different lipid dependence of various activities of microsomal glucose 6-phosphatase are discussed.
The lipid dependence of pyrophosphatase activity was studied by treatment of liver and hepatoma microsomes with phospholipase C from Cl. perfringens and B. cereus and a subsequent incorporation of various classes of phospholipids into the delipidated microsomes. Phospholipase C hydrolysis sharply lowers the pyrophosphatase activity of liver and hepatoma microsomes. The enzyme activity is restored after introduction of phospholipids into delipidated liver microsomes, the maximal effect being achieved on incorporation of phosphatidylcholine. All the phospholipids tested exerted the same reactivation effects on the delipidated microsomes of hepatoma. However, a more complete delipidation of hepatoma microsomes by phospholipase C hydrolysis and a subsequent organic solvent extraction revealed a specific dependence of the enzyme activity on phosphatidylserine.
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Modification of membrane lipid composition by lipid exchange proteins was used to study the lipid dependence of cytochrome P-450 activity in rat liver microsomes. The introduction of exogenous lysophosphatidylcholine into microsomal membranes decreased the capacity of cytochrome P-450 to demethylate dimethylaniline and dimethylaminoantipyrine and to hydroxylate aniline. A subsequent introduction of phosphatidylcholine resulted in an almost complete reactivation of the enzyme.
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The lipid dependence of hydroxylase and demethylase activities of microsomal cytochrome P-450 was studied, using purified phosphatidylcholine transfer protein from bovine liver. In the presence of this protein exogeneous phosphatidylcholine was shown to reactivate cytochrome P-450 inactivated earlier with lysophosphatidylcholine.