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S Parthasarathy

Publications and source records attributed to S Parthasarathy.

At least 181 records · Page 10Linked to original sources
PubMed1980

A rapid assay of acyl-coenzyme A:lysolecithin acyltransferase activity.

A simple and rapid procedure for the assay of acyl-coenzyme A:1-acyl-sn-glycero-3-phosphocholine acyltransferase (lysolecithin acyltransferase, LLAT [EC 2.3.1.23]) activity in crude enzyme preparations is described. The incubation system utilizes lysolecithin and [1-14C]-oleoyl-coenzyme A as substrates. Labeled fatty acid released due to accompanying acyl-coenzyme A hydrolase [EC 3.1.2.2]activity is first removed by di-isopropyl ether extraction. The labeled lecithin produced due to LLAT action is then quantitatively recovered by partition of the incubation medium with di-isopropyl ether-n-butanol 60:40 (v/v). Selective extraction of the labeled lecithin formed and avoidance of customary thin-layer chromatographic isolation procedures permits assay of LLAT activity with excellent accuracy at a substantial saving of time. The entire assay can be completed in less than 30 min as compared to 2-3 hrs when following conventional procedures.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1979

Ethanediol monoester hydrolysis by monoacylglycerol lipase of rat liver microsomes.

The hydrolysis of long-chain monoester of ethanediol by rat,liver subcellular fractions was investigated in order to define the carboxylic acid ester hydrolase involved and to localize the enzymic activity. We found that with 1-O-hexadecanoyl [U-14C]ethanediol as substrate, hydrolytic activity was foremost associated with the rough microsomal fraction. The pH optimum occurred at 8.5. The apparent Km and V values were 6.5 . 10(-4) M and 13 mumol/h per mg microsomal protein, respectively. Enzymic activity was inhibited by p-chloromercuribenzoate and by diisopropylfluorophosphate, whereas NaF was less effective and CaCl2 did not affect apparent activity. Amongst a number of carboxylic acid esters tested as substrate, only long-chain 1-acyl and 2-acyl glycerols inhibited acyl diol hydrolysis competitively (Ki approximately 0.9 mM). It was concluded that long-chain monoesters of ethanediol are hydrolyzed by the monoacyl glycerol lipase system associated with the rat liver microsomal fraction. Because diol monoester is also utilized by the cholinephosphotransferase system of liver to form highly lytic acyl diol phosphocholines, efficient diol monoester hydrolysis by monoglyceride lipase may be a significant step in regulating acyl diol phosphocholine levels in biological systems.

Animals↗
PubMed1978

Inhibition of diacylglycerol:CDPcholine cholinephosphotransferase activity by dimethylaminoethyl p-chlorophenoxyacetate.

Cholinephosphotransferase [EC 2.7.8.2] activity of rat liver microsomes, with 1,2-di-0-[3H]acyl glycerol or 1-0-hexadecanoyl [U-14C]ethanediol as substrate, was inhibited by N,N-dimethylaminoethyl p-chlorophenoxyacetate (centrophenoxine). Inhibition progressed in a linear fashion with increasing drug levels and was complete at 30 mM concentration. It appears that the microsomal enzyme was largely affected by the drug itself because the hydrolysis products of centrophenoxine, viz., N,N-dimethylaminoethanol and p-chlorophenoxyacetic acid, were less inhibitory.

Animals↗
PubMed1976

Evidence that acyl coenzyme A synthetase activity is required for repression of yeast acetyl coenzyme A carboxylase by exogenous fatty acids.

The cellular content of acetyl-CoA carboxylase [acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] in Saccharomyces cerevisiae is reduced by the addition of long-chain fatty acids to the culture medium. Mutant strains of S. cerevisiae defective in acyl-CoA synthetase [acid:CoA ligase (AMP-forming), EC 6.2.1.3] were isolated and used to determine whether fatty acid itself or a metabolite of fatty acid is more directly responsible for the repression of acetyl-CoA carboxylase. Cells of the mutant strains were capable of incorporating fatty acid to an extent comparable to that observed with the wild-type strain, but they accumulated markedly more of the incorporated fatty acid in the nonesterified form than did the wild-type cells. The level of acetyl-CoA carboxylase activity in the mutants, in contrast to that in the wild-type strain, was hardly affected by the addition of fatty acids to the medium. These results indicate that the activation of exogenous fatty acid is required for the repression of acetyl-CoA carboxylase, supporting the view that the repressive effect is mediated by some compound metabolically derived from fatty acid.

Acetate-CoA Ligase↗
PubMed1974

The mechanism of intestinal absorption of phosphatidylcholine in rats.

1. The mechanism of absorption of phosphatidylcholine was studied in rats by injecting into the intestine phosphatidylcholine specifically labelled either in the fatty acid or in the glycerol moiety or with (32)P, when considerable amounts of 1-acyl-lysophosphatidylcholine were found in the intestinal lumen. 2-([(14)C]Acyl)phosphatidylcholine gave markedly more radioactive unesterified fatty acids in the lumen, compared with the 1-([(14)C]acyl) derivative. Some of the radioactivity from either the fatty acid or the glycerol moiety of the injected phosphatidylcholine appeared in the mucosal triacylglycerols. 2. Injection of (32)P-labelled phosphatidylcholine or (32)P-labelled lysophosphatidylcholine led to the appearance of radioactive glycerylphosphorylcholine, glycerophosphate and P(i) in the mucosa. 3. Rat mucosa was found to contain a highly active glycerylphosphorylcholine diesterase. 4. It was concluded that the dietary phosphatidylcholine is hydrolysed in the intestinal lumen by the pancreatic phospholipase A to 1-acylglycerylphosphorylcholine, which on entering the mucosal cell is partly reacylated to phosphatidylcholine, and the rest is further hydrolysed to glycerylphosphorylcholine, glycerophosphate, glycerol and P(i). The fatty acids and glycerophosphate are then reassembled to give triacylglycerols via the Kennedy (1961) pathway.

Animals↗
PubMedDate not supplied

Increased glycodelin levels in gynecological malignancies.

Glycodelin, an immunosuppressive protein with contraceptive properties, is synthesized by a variety of tissues and cell types. The ability of reproductive tissues to synthesize glycodelin is of major interest in pregnancy and disease conditions. We studied glycodelin levels in subjects with malignant gynecological tumors and in control subjects. Using a polyclonal glycodelin antibody against the synthetic glycodelin peptide sequence, an enzyme-linked immunosorbent assay (ELISA) was devised to measure plasma glycodelin levels. The assay detected as much as 5 ng/ml of glycodelin. There was a significant increase in plasma glycodelin levels in endometrial > ovarian > cervical cancer subjects when compared to those of controls. Strong expression of mRNA and protein were found in the ovarian and endometrial tumor tissues. Given glycodelin's immunosuppressive abilities, increased level of glycodelin may facilitate tumor growth in gynecological malignancies.

Adolescent↗
PubMedDate not supplied

Oxidative stress in cardiovascular disease.

The oxidative hypothesis of cardiovascular disease (CVD) has undergone tremendous changes during the past few years. Innumerable new proatherogenic effects have been added to the existing list that could be attributed to oxidative stress. However, both animal and human trials with a variety of antioxidants have failed to establish unambiguously a protective role for antioxidants in the prevention of CVD. This could be because of poor choice and dosage of antioxidants, incompatible experimental models, oxidative metabolism of the antioxidant, unrealistic expectations, and other reasons. More importantly, recent studies suggest that oxidative stress also could induce antioxidant enzymes in both cell culture and in vivo systems. In lieu of the potential of known deterrents of CVD such as exercise, estrogens, and the consumption of polyunsaturated fatty acids to induce an oxidative stress, the possibility that natural enhancement of antioxidant defense in the artery could better serve to deter CVD cannot be ignored. Thus, if oxidative stress does play a role in CVD, it may be better, in the absence of suitable animal models that respond to antioxidants, to adhere to behavioral and dietary changes that have been shown to benefit CVD.

Cardiovascular Diseases↗
PubMedDate not supplied

Antisera and monoclonal antibodies specific for epitopes generated during oxidative modification of low density lipoprotein.

Increasing evidence indicates that low density lipoprotein (LDL) has to be modified to induce foam cell formation. One such modification, oxidation of LDL, generates a number of highly reactive short chain-length aldehydic fragments of oxidized fatty acids capable of conjugating with lysine residues of apoprotein B. By immunizing animals with homologous malondialdehyde-modified LDL (MDA-LDL), 4-hydroxynonenal-LDL (4-HNE-LDL), and Cu+(+)-oxidized LDL, we developed polyvalent and monoclonal antibodies against three epitopes found in oxidatively modified LDL. The present article characterizes an antiserum and monoclonal antibody (MAL-2 and MDA2, respectively) specific for MDA-lysine, and an antiserum and monoclonal antibody (HNE-6 and NA59, respectively) specific for 4-HNE-lysine. In addition, a monoclonal antibody (OLF4-3C10) was developed against an as yet undefined epitope generated during Cu++ oxidation of LDL. With these antibodies, we demonstrated that MDA-lysine and 4-HNE-lysine adducts develop on apo-lipoprotein B during copper-induced oxidation of LDL in vitro. The application of these antibodies for immunocytochemical demonstration of oxidized lipoproteins in atherosclerotic lesions of progressive severity is described in the companion article. These antibodies should prove useful in studying the role of oxidatively modified lipoproteins as well as other oxidatively modified proteins in atherogenesis.

Aldehydes↗
PubMedDate not supplied

Macrophage oxidation of low density lipoprotein generates a modified form recognized by the scavenger receptor.

Incubation of low density lipoprotein (LDL) with endothelial cells or smooth muscle cells overnight has resulted in an oxidative modification of LDL that results in its recognition by macrophages by way of the acetyl LDL receptor. In the present study, we examined whether macrophages themselves can oxidize and modify LDL in a manner similar to that of endothelial cells. Incubation of 125I-labeled LDL with resident or thioglycollate-elicited macrophages for 24 hours in Ham's F-10 medium resulted in the appearance of thiobarbituric acid (TBA) reactive materials and trichloroacetic acid (TCA) soluble radioactivity in the medium. The LDL harvested from these incubations showed increased electrophoretic mobility and was degraded rapidly when added to fresh macrophages as compared to LDL previously incubated in the absence of cells. These macrophage-induced modifications could be prevented if the first incubation was carried out in the presence of the antioxidant butylated hydroxytoluene (BHT) or in Dulbecco's modified Eagle's medium (DMEM). The degradation of 125I-labeled macrophage-modified LDL by macrophages was competitively inhibited by unlabeled acetyl LDL or unlabeled endothelial cell-modified LDL but not by native LDL, indicating that the degradation was mediated by the acetyl LDL receptor.

Animals↗
PubMedDate not supplied

Decrease in reactive amino groups during oxidation or endothelial cell modification of LDL. Correlation with changes in receptor-mediated catabolism.

The monocyte/macrophage appears to be the precursor of many of the lipid-laden cells in atherosclerotic lesions, but the mechanism by which these cells accumulate cholesterol to become foam cells remains unclear. We have previously reported that cultured endothelial cells can modify low density lipoprotein (LDL) in a manner that leads to rapid uptake by the acetyl LDL receptor of macrophages. This modification involves free radical-induced peroxidation of LDL and is accompanied by many changes in the physicochemical properties of LDL including increased electrophoretic mobility, increased density, decreased content of esterified cholesterol, hydrolysis of phosphatidylcholine, and fragmentation of apolipoprotein B. Under conditions highly favorable to oxidation, a similar modification can occur even in the absence of cells. In the present studies, oxidation of LDL simply by exposure to 5 microM Cu++ resulted in a modification that was indistinguishable from that produced by endothelial cells. Moreover, it was demonstrated that LDL oxidation by either method is accompanied by a marked decreased in amino group reactivity, comparable to that seen with the chemical modifications of LDL that lead to recognition by the acetyl LDL receptor. Inhibitors of proteolytic enzymes did not reduce fragmentation of apolipoprotein B during oxidation. The rate of catabolism of intravenously injected oxidized LDL in guinea pigs was very rapid, and over 80% of the degradation occurred in the liver. The studies demonstrate that all of the changes associated with endothelial cell modification of LDL can be attributed to oxidation. The cells can, however, promote oxidation under conditions where it would otherwise occur very slowly.(ABSTRACT TRUNCATED AT 250 WORDS)

Amines↗
PubMedDate not supplied

Oxidative modification of beta-very low density lipoprotein. Potential role in monocyte recruitment and foam cell formation.

Oxidative modification of low density lipoprotein (LDL) generates a form that is degraded much more rapidly by macrophages and may thus be more atherogenic than unoxidized LDL. Recently, we provided evidence that oxidative modification of LDL may play a significant role in the generation of fatty streaks in the LDL receptor-deficient rabbit. The major lipoprotein in cholesterol-fed animals is the beta-very low density lipoprotein (beta-VLDL). Since beta-VLDL is avidly taken up by macrophages, it could lead to foam cell formation without the need for oxidative modification or modification of other kinds. However, the present studies show that beta-VLDL can be oxidized by incubation with endothelial cells or with copper ions. Oxidized beta-VLDL was degraded by macrophages at about twice the rate of unoxidized beta-VLDL, and it stimulated cholesterol esterification twice as much as unoxidized beta-VLDL. The degradation of oxidized beta-VLDL was inhibited either by oxidized beta-VLDL itself or by oxidized LDL, but not by unoxidized beta-VLDL. beta-VLDL was chemotactic for human monocytes and contained significant amounts of lysophosphatidylcholine, previously shown to be a chemotactic agent. In summary, oxidized LDL is degraded by macrophages proportionately more than oxidized beta-VLDL as compared to the unmodified lipoproteins. However, the twofold increase may, nevertheless, be significant in the atherogenicity of beta-VLDL.

Animals↗