Oxidative Phosphorylation in Pea Cotyledon Submitochondrial Particles

Abstract

Mitochondria and submitochondrial particles (SMP) from pea cotyledons [cv. Homesteader] catalyzed oxidative phosphorylation as measured by 32Pi 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 (Km = 0.18 mM). ADP kinetics gave a biphasic curve with Km values of about 4.8 and 160 mM. O2 uptake and ATP synthesis had a pH maximum of 7.6 while the ratio of .mu.mol phosphate esterified to microatoms O2 taken up was highest at pH 7.2. NaCl inhibited both ATP synthesis and O2 uptake but stimulated the ATPase reaction. The SMP also catalyzed a slow ATP-phosphate exchange reaction.