Inhibition of the Plastidic Pyruvate Dehydrogenase Complex in Isolated Plastids of Oat

Abstract

The, activity of the plastidic pyruvate dehydrogenase complex (pPDHC) is one source of acetyl-CoA in plastids of higher plants needed for de novo fatty acid biosynthesis. This plastidic enzyme reaction is specifically inhibited by acetylmethylphosphinate (AMPI), a compound which had hitherto been known only as an inhibitor of the mitochondrial pyruvate dehydrogenase complex (mPDHC). In the test system of isolated intact oat plastids (Avena sativa) [2-14C,]pyruvate was used for de novo fatty acid biosynthesis. The incorporation of label from [2-14C,]pyruvate in fatty acids was inhibited by AMPI iNADose-dependent manner. The inhibition rose with increasing preincubation time of plastids with the inhibitor.I50 values for the inhibition of de novo fatty acid biosynthesis from [2-14C,]pyruvate by AMPI for isolated etioplasts and chloroplasts were 4.5 and 80 μm. respectively. The activity of the pPDFIC decreased during greening of oat seedlings, as is seen from the decreasing incorporation of [2-14C,]pyruvate into fatty acids during the light-induced transformation of etioplasts into chloroplasts. In contrast to the decreasing pPDHC activity, the activity of the plastidic acetyl-CoA synthetase (ACS), which transfers acetate to acetyl-CoA, rose parallel to the transformation of etioplasts into chloroplasts. During the assay time of 20 min we could not detect an incorporation of radiolabel from pyruvate or acetate intoß-carotene or any other carotenoid. © 1994, Walter de Gruyter. All rights reserved.