Pyruvate dehydrogenase complex and acetyl-CoA carboxylase in pea root plastids: their characterization and role in modulating glycolytic carbon flow to fatty acid biosynthesis

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The pyruvate dehydrogenase complex (PDC) and acetyl-CoA carboxylase (ACC, EC 6.4.1.2) have been characterized in pea root plastids. PDC activity 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 Tricine (pH 8.0) and represents approximately 47% of the total cellular activity. ACC activity was greatest in the presence of 1.0 mM acetyl-CoA, 4 mM NaHCO3 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 inhibited 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 inhibited ACC, but had essentially no effect on PDC. Palmitoyl-CoA inhibited both enzymes while PA and Lyso-PA inhibited PDC, but stimulated ACC. The results presented support the hypothesis that PDC and ACC function in a co-ordinated fashion to promote glycolytic carbon flow to fatty acid biosynthesis in pea root plastids.