PYRUVATE-DEHYDROGENASE COMPLEX AND ACETYL-COA CARBOXYLASE IN PEA ROOTPLASTIDS - THEIR CHARACTERIZATION AND ROLE IN MODULATING GLYCOLYTIC CARBON FLOW TO FATTY-ACID BIOSYNTHESIS

The pyruvate dehydrogenase complex (PDC) and acetyl-CoA carboxylase (A CC, EC 6.4.1.2) have been characterized in pea root plastids. PDC acti vity was optimum in the presence of 1.0 mM pyruvate, 1.5 mM NAD(+), 0. 1 mM CoA, 0.1 mM TPP, 5 mM MgCl2, 3.0 mM cysteine-HCl, and 0.1 M Trici ne (pH 8.0) and represents approximately 47% of the total cellular act ivity. ACC activity was greatest in the presence of 1.0 mM acetyl-CoA, 4 mM NaHCO3, 3 mM ATP, 10 mM MgCl2, 2.5 mM dithiothreitol, and 100 mM Tricine (pH 8.0). Both enzymes were stimulated by reduced sulphydryl reagents and inhibited by sulphydryl inhibitors. ACC was also inhibite d by malonyl-CoA while PDC was inhibited by both malonyl-CoA and NADH. Both enzymes were stimulated by DHAP and UDP-galactose while ACC was also stimulated by PEP and F1,6P. Palmitic acid and oleic acid both in hibited ACC, but had essentially no effect on PDC. Patmitoyl-CoA inhib ited both enzymes while PA and Lyse-PA inhibited PDC, but stimulated A CC. The results presented support the hypothesis that PDC and ACC func tion in a co-ordinated fashion to promote glycolytic carbon flow to fa tty acid biosynthesis in pea root plastids.