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The relationship between palmitoyl-coenzyme A synthetase activity and esterification of sn-glycerol 3-phosphate by the microsomal fraction of guinea-pig intestinal mucosa.

ABSTRACT: 1. With microsomal fractions of guinea-pig intestinal mucosa the mean specific activity of palmitoyl-CoA synthetase was approx. 1.3-fold the esterification of sn-glycerol 3-phosphate with palmitoyl-CoA generated by the endogenous synthetase. The latter activity was approx. 2.5- and 5-fold that when palmitoyl-CoA was generated from palmitoylcarnitine or when it was added directly to the assay system. 2. There were significant correlations (P<0.001) between the specific activities of palmitoyl-CoA synthetase and glycerolipid synthesis from either palmitate or palmitoylcarnitine. 3. The mean molar composition of glycerolipid synthesized from palmitate or palmitoylcarnitine was approx. 18% lysophosphatidate, 75% phosphatidate and 7% neutral lipid. 4. Glycerolipid synthesis from palmitate was inhibited by 80-90% after preincubation of microsomal fractions at 37 degrees C for 40min and was caused by inactivation of palmitoyl-CoA synthetase. 5. Addition of 100-400mm-KCl inhibited palmitoyl-CoA synthetase activity and glycerolipid synthesis from palmitate but stimulated glycerol phosphate acyltransferase activity. 6. Diversion of palmitoyl-CoA synthesized by the endogenous synthetase to palmitoylcarnitine resulted in an almost stoicheiometric decrease in glycerolipid synthesis. 7. Addition of rac-1-monopalmitin promoted utilization of palmitoyl-CoA by the monoglyceride pathway but did not inhibit phosphatidate biosynthesis. 8. With rate-limiting concentrations of CoA and Mg(2+) the relative decreases in velocity for palmitoyl-CoA synthetase and glycerolipid synthesis from palmitate were almost identical. However, low concentrations of palmitate and ATP produced greater decreases in synthetase activity than in glycerolipid synthesis. 9. There appears to be a fine balance between the activities of palmitoyl-CoA synthetase and glycerol phosphate acyltransferase, with neither activity being in excess with respect to phosphatidate synthesis.

SUBMITTER: Brindley DN

PROVIDER: S-EPMC1177646 | biostudies-other | 1973 Apr

REPOSITORIES: biostudies-other

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Project description:1. The specific activities for palmitoyl-CoA synthetase and for sn-glycerol 3-phosphate esterification, with palmitoyl-CoA generated either by the endogenous synthetase or from palmitoyl-(-)-carnitine, CoA and excess of carnitine palmitoyltransferase, were measured with rat liver mitochondria. 2. The mean specific activity of palmitoyl-CoA synthetase was approximately five- and seven-fold the rates of sn-glycerol 3-phosphate esterification from palmitate and palmitoyl-(-)-carnitine respectively. No significant correlation was found in different rats between the activities of palmitoyl-CoA synthetase and sn-glycerol 3-phosphate esterification from either acyl precursor. However, there was a significant correlation (r=0.83, P<0.001) between the rates of glycerolipid synthesis from palmitate and palmitoyl-(-)-carnitine. 3. The mean molar composition of the glycerolipid synthesized from palmitate was 58% lysophosphatidate, 31% phosphatidate and 11% neutral lipid. With palmitoyl-(-)-carnitine the equivalent values were 70, 23 and 7%, which were significantly different. 4. When palmitoyl-CoA synthetase had been inactivated by 60-70% after preincubation of mitochondria at 37 degrees C, it became rate-limiting in glycerolipid biosynthesis. Additions of 1-5mm-ATP prevented inactivation of palmitoyl-CoA synthetase. 5. Preincubation also inhibited the oxidation of palmitate, palmitoyl-CoA, palmitoyl-(-)-carnitine and malate plus glutamate. These inhibitions could not be prevented by addition of ATP. 6. Diversion of palmitoyl-CoA to form palmitoyl-(-)-carnitine did not inhibit sn-glycerol 3-phosphate esterification. 7. The palmitoyl-CoA pool synthesized by the palmitoyl-CoA synthetase was augmented by adding partially purified synthetase or carnitine palmitoyltransferase and palmitoyl-(-)-carnitine. No stimulation of palmitate incorporation into glycerolipids occurred. 8. At low concentrations of Mg(2+), palmitate, ATP and CoA the velocity with palmitoyl-CoA synthetase decreased more than that of glycerolipid synthesis from palmitate. 9. It is concluded that in the presence of optimum substrate concentrations the activity of sn-glycerol 3-phosphate acyltransferase and not of palmitoyl-CoA synthetase is rate-limiting in the synthesis of phosphatidate and lysophosphatidate in isolated rat liver mitochondria.

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The relationship between palmitoyl-coenzyme A synthetase activity and esterification of sn-glycerol 3-phosphate by the microsomal fraction of guinea-pig intestinal mucosa.

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