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Biomedical subjects

A K Hajra

Publications and source records attributed to A K Hajra.

12 recordsLinked to original sources
PubMed1979

Subcellular localization of acyl coenzyme A: dihydroxyacetone phosphate acyltransferase in rat liver peroxisomes (microbodies).

Upon differential centrifugation of rat liver homogenate, the enzyme acyl-CoA:dihydroxyacetone-phosphate acyltransferase (EC 2.3.1.42) was found to be localized in the light mitochondrial (L) fraction which is enriched with lysosomes and peroxisomes. Peroxisomes were separated from lysosomes in a density gradient centrifugation using rats which were injected with Triton WR 1339. By comparing the enzyme distribution with the distribution of different marker enzymes, it was concluded that dihydroxyacetone phosphate acyltransferase is primarily localized in rat liver peroxisomes (microbodies). Similarly, the enzyme acyl dihydroxyacetone-phosphate:NADPH oxidoreductase (EC 1.1.1.101) was shown to be enriched in the peroxisomal fraction, although a portion of this reductase is also present in the microsomal fraction.

Acyltransferases↗
PubMed1979

Stereochemical specificity of the biosynthesis of the alkyl ether bond in alkyl ether lipids.

The stereochemical course of the formation of the alkyl ether bond in alkyl ether lipids was investigated through the synthesis of stereospecifically labeled acyl R- or S-[1-3H]dihydroxyacetone 3-phosphate (DHAP) starting from L-glyceraldehyde. It was demonstrated directly that the formation of the alkyl ether bond results in the stereospecific exchange of the pro-R C-1 hydrogen of DHAP with a proton of water. The configuration of the hydrogen that is retained on C-1 after formation of the alkyl ether bond was also investigated. The alkyl ether lipid was degraded, and the DHAP backbone isolated as glycerol, converted to DHAP via glycerol 3-phosphate and treated with either aldolase or triose phosphate isomerase. The results demonstrated that the retained hydrogen on C-1, which was pro-S in the starting substrate, was pro-S in the product alkyl ether.

Carbon Radioisotopes↗
PubMed1977

1-Alkyl-sn-glycero-3-phosphate: acyl-CoA acyltransferase in rat brain microsomes.

1-Alkyl-sn-glycero-3-phosphate:acyl-CoA acyltransferase activity was found in six rat tissues: heart, spleen, brain, kidney, liver, and lung. The enzyme in rat brain showed highest specific activity in the microsomal fraction and its properties were studied in detail. Triton X-100 and bovine serum albumin were found to stimulate the activity of the enzyme. It was found that Triton X-100 affects the acyltransferase activity differentially depending on the acyl-CoA donor. Albumin reversed the inhibition caused by a high concentration of 1-alkyl-sn-glycero-3-phosphate. The enzyme was shown to be stereospecific in acylating the alkylglycerophosphate substrate. Only the 1-alkyl-sn-glycero-3-phosphate isomer, not the other optical enantiomer, was active with brain acyltransferase. Evidence is presented to show that this enzyme is different from 1-acyl-sn-glycero-3-phosphate:acyl-CoA acyltransferase. Investigations of the specificity of the brain acyltransferase activity for different acyl-CoA species (16:0, 18:0, 18:2, 20:4, 22:4, 22:6) showed a selectivity which was dependent on the alkylglycerophosphate concentration. At low 1-alkyl-sn-glycero-3-phosphate concentration the enzyme selected polyunsaturated acyl-CoA species over saturated species. Providing a low but continuous amount of 1-alkyl-sn-glycero-3-phosphate to the acyltransferase was accomplished by the in situ enzymatic reduction of alkyldihydroxyacetone phosphate with NADPH in the incubation mixtures. The acyl composition of ether-containing phosphoglycerides in rat brain microsomes, as well as the free fatty acid composition, was determined. Alkenylacylglycerophosphorylethanolamine contains a high percentage of 22:6 ester, and alkenylacylglycerophosphorylcholine contains a large amount of 16:0 ester. Comparison of the acyl-CoA specificity of 1-alkyl-sn-glycero-3-phosphate acyltransferase and ether/glycerolipid acyl composition suggests that this acyltransferase could partially determine the composition of acyl groups in ether lipids.

Acetyltransferases↗
PubMed1976

Gonadotropin receptors in plasma membranes of bovine corpus luteum. II. Role of membrane phospholipids.

The role of phospholipids in the binding of 125I-choriogonadotropin to bovine corpus luteum plasma membranes has been investigated with the use of purified phospholipase A and phospholipase C to alter membrane phospholipids. The phospholipase C-digested plasma membrane preparation showed 85 to 90% inhibition of 125I-choriogonadotropin binding activity when 70% of the membrane phospholipid was hydrolyzed. Similarly treatment of plasma membranes with phospholipase A resulted in 45 to 55% hydrolysis of membrane phospholipid and almost 75% inhibition of receptor activity. Both these enzymes hydrolyzed membrane-associated phosphatidylcholine to a greater extent than phosphatidylethanolamine and phosphatidylserine. Phosphorylaminoalcohols of phospholiphase C end products were completely released into the medium, while phospholipase A by-products remained associated with plasma membranes. Addition of a phospholipids suspension or liposomes to plasma membranes pretreated with phospholipase A and C did not restore gonadotropin binding activity. Soluble phosphorylcholine, phosphorylethanolamine, and phosphorylserine and insoluble diglyceride products of phospholipase C action had no effect on receptor activity. In contrast, end products of the phospholipase A action, such as lysophosphatides and fatty acids, inhibited both on the membrane-associated and solubilized receptor activity. Lysophosphatidylcholine was the most effective end product inhibiting the binding of gonadotropin to the receptor, followed by lysophosphatidylethanolamine and lysophosphatidylserine. The inhibitory effects of phospholipase A or lysophosphatides were completely reversed upon removal of membrane-bound phospholipid end products by washing the membranes with defatted bovine serum albumin. However, phospholipase C inhibition could not be overcome by defatted albumin washings. Solubilization of plasma membranes with detergents which had been pretreated with phospholipase C partially restored the inhibited activity. It is concluded that the phospholipase-mediated inhibition of gonadotropin binding activity was due to hydrolysis and alterations of the phospholipid environment in the case of phospholipase C and by direct inhibition by end products in the case of phospholipase A.

Animals↗
PubMed1976

Incorporation of D-[3-3H, U-14C] glucose into glycerolipid via acyl dihydroxyacetone phosphate untransformed and viral-transformed BHK-21-c13 fibroblasts.

Untransformed BHK-21-c13 fibroblasts as well as 4 polyoma-transformed strains were incubated with D-[U-14C,3-3H]glucose. This substrate generates intracellular labeled glycerol, and also [4-3H]NADPH via the phosphogluconate oxidative pathway. The latter selectively transfers hydrogen to C-2 of glycerol in glycerolipid via the acyl dihydroxyacetone phosphate pathway. After incubation, the distribution of radioactivity and the ratios of 3H/14C at the three positions of recovered glycerol were determined in sn-glycerol 3-phosphate, saponifiable glycerolipids, alkyl ether glycerolipids, and plasmalogens. In each of the cell types examined, 3H in the sn-1 position of glycerol in the recovered ether-containing glycerolipids was negligible, yet this position contained most of the recovered 3H in sn-glycerol 3-phosphate and saponifiable glycerolipids. The 3H/14C ratio in position 2 of glycerol, measured at various incubation times, was from 5- to 200-fold greater in the saponifiable glycerolipids than in free sn-glycerol 3-phosphate. The ratio in position 2 of ether-containing glycerolipids was the same or greater than that in the saponifiable glycerolipids in all of the cell types employed. A similar pattern in the 3H/14C ratio was observed when BHK-21-c13 cells were incubated with D-[U-14C,1-3H]glucose. These observations demonstrate significant participation of the acyl dihydroxyacetone phosphate pathway in glycerolipid synthesis in BHK cells.

Cell Line↗