ATP synthesis driven by α-keto acid-stimulated alternative oxidase in pea leaf mitochondria

The electrical potential difference (A¥) generation and ATP synthesis due to a-ketoacid stimulated alternative oxidase activity in pea leaf mitochondria, energized by malateplus glutamate, was studied. In the absence of a-ketoacids, DF was ca. 60% collapsed by KCN or antimycin A (AA), while the remaining part (ca.30%was dissipated by salicylhydroxamicacid (SHAM). The presence of a-ketoacids (pyruvate or iodoacetate),known to stimulate the alternative oxidase,caused a decrease in the KCN- or AA-sensitive component of A'F(ca.30%), which was accompanied by an increase in the SHAM-sensitive one. When mitochondria were energized by exogenous NADH, succinate or duroquinol, AY was completely collapsed by KCN or AA, either in the presence or absence of a-ketoacids. ADP partially collapsed the-sensitive component of AT, and oligomycin restored this dissipation. In the presence of pyruvate or iodoacetate, ATP content in KCN-treated mitochondria was ca.40 of control,while that in SHAM plus KCN-inhibited mitochondria was negligible. AOP stimulated oxygen uptake only in the presence of KCN(respiratory control ratio = 1.7), but not in the presence of KCN plus SHAM. It is concluded that a-ketoacids, stimulating the oxidation of NAD-linked substrates through the alternative oxidase, lead to an increase in the SHAM-sensitive component of zliP via complex I, thus increasing the contribution of this pathway to ATP synthesis when the cytochrome oxidase is restricted.