THE REGULATION OF PYRUVATE-DEHYDROGENASE ACTIVITY IN PEA LEAF MITOCHONDRIA - THE EFFECT OF RESPIRATION AND OXIDATIVE-PHOSPHORYLATION

The regulation of the pea (Pisum sativum) leaf mitochondrial pyruvate dehydrogenase complex by respiratory rate and oxidative phosphorylatio n has been investigated by measuring the respiratory activity, the red ox poise of the quinone pool (Q-pool), and mitochondrial pyruvate dehy drogenase (mtPDC) activity under various metabolic conditions. It was found that, under state 4 conditions, mtPDC activity was unaffected by either the addition of succinate, 2-oxoglutarate, or glycine or the o verall respiratory rate and redox poise of the Q-pool but was partiall y inhibited by NADH due to product inhibition. In the presence of ADP significant inactivation of PDC, which was sensitive to oligomycin, wa s observed with all substrates, apart from pyruvate, suggesting that i nactivation was due to ATP formation. Inactivation of PDC by ADP addit ion was observed even in the presence of carboxyatractyloside, an inhi bitor of the ATP/ADP translocator, suggesting that other mechanisms to facilitate the entry of adenylates, in addition to the adenylate carr ier, must exist in plant mitochondria.