MICROSOMAL-ASSOCIATED GLYCEROPHOSPHATE ACYLTRANSFERASE ACTIVITY IN GERMINATING SOYBEANS

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Abstract
Acyl CoA:sn-glycero-3-phosphate O-acyltransferase (glycerophosphate acyltransferase, EC 2.3.1.15) catalyzes the acylation of glycero-3-phosphate to form lysophosphatidic acid. This enzyme catalyzes the first committed step in the biosynthesis of phospholipids and acylglycerols in soybeans. Glycerophosphate acyltransferase was predominatly associated with the microsomal fraction of germinating soybeans. The pH optimum for the reaction was 7.0. The enzyme exhibited saturation kinetics for glycero-3-phosphate (Km of 0.2 mM) and palmitoyl CoA (Km of 6.4 μM). A variety of acyl CoA derivatives served as substrates for the enzyme. Palmitoyl CoA was the most effective acyl CoA substrate. The addition of the nonionic detergent Triton X-100 inhibited glycerophosphate acyltransferase activity. Thioreactive agents inhibited the enzyme indicating that a sulphydryl group is essential for activity. The activation energy for the reaction was 8.8 Kcal per mole. The microsomal enzyme was reasonably stable to temperatures up to 70° C.