[The relationship between palmitoyl-coenzyme A synthetase activity and esterification of sn-glycerol 3-phosphate in rat liver mitochondria].
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.
D000217:Acyltransferases / Q000378:metabolism; D000818:Animals; D002331:Carnitine / Q000378:metabolism; D003066:Coenzyme A Ligases / Q000302:isolation & purification / Q000378:metabolism*; D005994:Glycerophosphates / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010169:Palmitic Acids / Q000378:metabolism; D051381:Rats; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors; D014316:Tritium
D005994:Glycerophosphates; D010169:Palmitic Acids; D014316:Tritium; D000217:Acyltransferases; D003066:Coenzyme A Ligases; D002331:Carnitine