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Biomedical subjects

C M Gupta

Publications and source records attributed to C M Gupta.

At least 91 records · Page 5Linked to original sources
PubMed1981

Carbamyl analogs of phosphatidylcholines. Synthesis, interaction with phospholipases and permeability behavior of their liposomes.

A novel class of phospholipase-resisting phosphatidylcholine analogs, in which the C-2 ester group or both C-1 and C-2 ester groups have been replaced by carbomyloxy functions (Formula--see text), have been synthesized. These lipids were not degraded by phospholipase A2, while complete hydrolysis occurred with phospholipase C. Ultrasonic irradiation of the aqueous dispersions of the phospholipids in the presence as well as in the absence of cholesterol resulted in the formation of closed bilayer structures as evidenced by negative staining electron microscopy and also by their ability to entrap [14C]glucose. The leakage rates of glucose at 37 degrees C from liposomes of these compounds have also been measured. Liposomes consisting of 1,2-dipentadecanylcarbamyloxy-sn-glycero-3-phosphorylcholine were found to be more leaky (2.1%/h) as compared to the liposomes of 1-palmitoyl-2-pentadecanylcarbamyloxy-sn-glycero-3-phosphorylcholine (0.5%/h). Moreover, inclusion of cholesterol (33 mol%) into the bilayers of the former phospholipid had no effect on the leakage rate (2.4%/h) while it effectively reduced permeability of the latter (0.22%/h). These phosphatidylcholines are useful for studying the possible role of phospholipases in the capture and lysis of liposomes in vivo.

Cholesterol↗
PubMed1981

Interaction of cholesterol with photoactivable phospholipids in sonicated vesicles.

Photoactivable phospholipids containing either alpha-diazo-beta-trifluoropropionyloxy or m-diazirinophenoxyl groups in the omega-positions of sn-2 fatty acyl chains were synthesized and incorporated into sonicated vesicles containing 33 mol% of cholesterol. Photolysis of the vesicles at 350 nm produced covalent cross-links between the synthetic phospholipids and cholesterol. The cross-linked products obtained using [14C]cholesterol were characterized by their chromatographic behavior, cleavage on phospholipase A2 treatment, base-catalyzed transesterification and mass spectral measurements. The cross-linking was shown not to involve the 3-beta-hydroxyl group of cholesterol, and it was concluded that the reactive carbene intermediates formed from the photolabels inserted into the hydrocarbon skeleton of cholesterol in the bilayer. The extent of cross-linking obtained was comparable to that observed previously using phospholipids alone, indicating that no lateral phase separation occurred. The present approach is promising for further precise studies of the molecular interactions between cholesterol and phospholipids in biological membranes.

Chemical Phenomena↗
PubMed1981

Involvement of malarial proteases in the interaction between the parasite and host erythrocyte in Plasmodium knowlesi infections.

The effect of protease inhibitors obtained from the culture filtrates of actinomycetes (pepstatin, chymostatin, leupeptin, phosphoramidon and elastatinal) on the in vitro invasion of erythrocytes from rhesus and assamese monkeys by Plasmodium knowlesi merozoites was studied. The presence of these inhibitors had no effect on release of merozoites from schizonts but inhibited entry of the parasite into the red cell. Thus, at 50 micrograms/ml, chymostatin and leupeptin completely blocked the invasion whereas pepstatin and elastatinal showed 50% inhibition. Phosphoramidon at this concentration gave only 30% inhibition. Pretreatment of the erythrocytes with these inhibitors did not block invasion. Also, the intracellular development of the parasite was totally unaffected in the presence of these agents. These results suggested that proteases of merozoites might play some crucial role in the invasion process.

Animals↗
PubMed1980

Phospholipids containing photoactivable groups in studies of biological membranes.

Photoactivable carbene precursors, aryl diazirines and trifluorodiazopropionates, were incorporated synthetically into the omega-positions of fatty acids, which were used to synthesize phospholipids. Extensive intermolecular C--H insertion reactions were demonstrated by photolysis of liposomes prepared from the above phospholipids. Structural analysis of the cross-linked products showed that the predominant sites of cross-linking were in the expected positions within the bilayer. Studies on the topography of a number of membrane proteins using the above phospholipids were initiated. Cross-linking of the photoactivable phospholipids to membrane-embedded proteins, glycophorin A, cytochrome b5, and gramicidin A, was demonstrated.

Animals↗
PubMed1979

Intermolecular crosslinking of fatty acyl chains in phospholipids: use of photoactivable carbene precursors.

Phospholipids containing photolysable carbene precursors (beta-trifluoro-alpha-diazopropionoxy and m-diazirinophenoxy groups) in omega-positions of sn-2 fatty acyl chains were prepared. Photolysis of their vesicles produced crosslinked products in 40-60% yields. Crosslinking was mostly intermolecular and occurred by carbene insertion into the C-H bonds of a second fatty acyl chain. Crosslinking products were characterized by (i) their gel permeation behavior, (ii) analysis of products formed by base-catalyzed transesterification, (iii) degradation with phospholipases A2 and C, (iv) gas chromatography/mass spectrometry, and (v) use of mixtures of phospholipids carrying the carbene precursors and a phospholipid containing radioactively labeled fatty acyl groups. Nitrenes generated from the aliphatic or aromatic azido groups in phospholipids were unsatisfactory for forming crosslinks by insertion in C-H bonds.

Chemical Phenomena↗
PubMed1979

Sites of intermolecular crosslinking of fatty acyl chains in phospholipids carrying a photoactivable carbene precursor.

Sonicated vesicles of 1-fatty acyl-2-omega-(2-diazo-3,3,3-trifluoropropionoxy) fatty acyl sn-glycero-3-phosphoryl-cholines were shown recently to form intermolecular crosslinks by insertion of the photogenerated carbene into a C-H bond of a neighboring hydrocarbon chain. We now report that photolysis of multilamellar dispersions gives a second series of products in which carbene insertion is accompanied by elimination of a molecule of hydrogen fluoride. The sites of crosslinking in the latter compounds have been studied by mass spectrometry using phospholipids with varying chain lengths of the fatty acyl groups carrying the carbene precursor. The patterns observed show that the point of maximum crosslinking is consistent with the recent conclusion that in phospholipids the sn-2 fatty acyl chain trails the sn-1 chain by 2-4 atoms.

Journal Article↗
PubMed1977

Glycerophospholipid synthesis: improved general method and new analogs containing photoactivable groups.

Current methods for phospholipid synthesis involving acylation of sn-glycero-3-phosphorylcholine, lysolecithins, and related glycerophosphate esters are not satisfactory. With N,N-dimethyl-4-aminopyridine as a catalyst and moderate amounts of fatty acid anhydrides (1.2-1.5 mol equiv per OH group), diacyl or 1,2-mixed diacylphosphatidylcholines, N-protected phosphatidylethanolamines, and phosphatide acids now can be conveniently prepared in high yields (75-90%). New phospholipids containing photoactivable groups, such as trifluorodiazopropionyl, diazirinophenoxy, 2-nitro-4-azidophenoxy, m-azidophenoxy, and alpha, beta-unsaturated keto groups, in the fatty acyl chains have been prepared. These phospholipids are of interest in studies of lipid-lipid and lipid-protein interactions in biological membranes.

Acylation↗