Oxidative Phosphorylation in Pea Cotyledon Submitochondrial Particles

Mitochondria and submitochondrial particles (SMP) from pea cotyledons were shown to catalyze oxidative phosphorylation as measured by (32)Pi uptake into phosphate esters. ATP synthesis was sensitive to the electron transport inhibitor KCN, the uncoupler carbonyl cyanide m-chlorophenylhydrazone, and the coupling factor inhibitor oligomycin. Experiments with the adenine nucleotide translocator inhibitor atractyloside indicated the SMP were inside-out. Mersalyl completely inhibited ATP synthesis by SMP, and a separate experiment indicated that mersalyl has a direct effect on the ATPase complex. The kinetics of ATP synthesis indicated a high affinity for phosphate (K(m) = 0.18 millimolar). ADP kinetics gave a biphasic curve with K(m) values of about 4.8 and 160 micromolar. O(2) uptake and ATP synthesis had a pH maximum of 7.6 while the ratio of micromoles phosphate esterified to microatoms O(2) taken up was highest at pH 7.2. Sodium chloride inhibited both ATP synthesis and O(2) uptake but stimulated the ATPase reaction. The SMP also catalyzed a slow ATP-phosphate exchange reaction.