Elementary plant Biochemistry and Biotechnology (2+1)

Biosynthesis of Triacylglycerols

• Triacylglycerols are not synthesised by reversal of lipolysis. They are synthesisd by a different mechanism in which both glycerol and fatty acids are activated by ATP before they are incorporated into acylglycerols.

Activation of glycerol

• Glycerol kinase catalyses the activation of glycerol to glycerol 3 phosphate. If glycerol kinase is found in low quantity or absent, glycerol 3 phosphate will be formed from dihydroxyacetone phosphate obtained from glycolysis and this reaction is catalysed by the enzyme glycerol 3 phosphate dehydrogenase.

Activation of fatty acids

• Fatty acids are activated to acyl CoA by the enzyme acyl CoA synthetase, utilizing ATP and CoASH. Two molecules of acyl CoA combine with glycerol 3 phosphate to form 1,2 diacylglycerol phosphate. Formation of 1,2 diacyl glycerol phosphate takes place in two stages, catalysed by glycerol 3 phosphate acyl transferase and then by 1 acyl glycerol 3- phosphate acyl transferase. The phosphate group is removed from 1,2 diacyl glycerol phosphate by phosphatidate phosphatase to form 1,2 diacyl glycerol.Triacylglycerols are finally formed by esterification of one or more molecule of acyl CoA with the diacylglycerol.

Alternative pathway for triacylglycerol biosynthesis

• In this pathway, dihydroxyacetone phosphate from glycolysis is reduced by NADPH, acylated and converted to lysophosphatidate.This pathway accounts for less than 10% of total triacylglycerol synthesis.