ATP SYNTHESIS DRIVEN BY ALPHA-KETO ACID-STIMULATED ALTERNATIVE OXIDASE IN PEA LEAF MITOCHONDRIA

The electrical potential difference (Delta Psi) generation and ATP syn thesis due to alpha-keto acid-stimulated alternative oxidase activity in pea leaf mitochondria, energized by malate plus glutamate, was stud ied. In the absence of alpha-keto acids, Delta Psi was ca. 60% collaps ed by KCN or antimycin A (AA), while the remaining part (ca. 30%) was dissipated by salicylhydroxamic acid (SEAM). The presence of alpha-ket o acids (pyruvate. or iodoacetate), known to stimulate the alternative oxidase, caused a decrease ill the KCN- or AA-sensitive component of Delta Psi (ca. 30%), which was accompanied by an increase in the SHAM- sensitive one. When mitochondria were energized by exogenous NADH, suc cinate or duroquinol, Delta Psi completely collapsed by KCN or AA, eit her in the presence or absence of alpha-keto acids. ADP partially coll apsed the SHAM-sensitive component of Delta Psi, and oligomycin restor ed this dissipation. In the presence of pyruvate or iodoacetate, ATP c ontent in KCN-treated mitochondria was ca. 40% of control, while that in SHAM plus KCN-inhibited mitochondria was negligible. ADP stimulated . oxygen uptake only in the presence of KCN (respiratory control ratio = 1.7), but not in the presence of KCN pins SHAM. It is concluded tha t alpha-keto acids, stimulating file oxidation of NAD-linked substrate s through the alternative oxidase, lead to an increase in tile SHAM-se nsitive component of Delta Psi via complex I, thus increasing the cont ribution of this pathway to ATP synthesis when the cytochrome oxidase is restricted.