Plant and Cell Physiology, 1997, Vol. 38, No. 12 1368-1374
© 1997
ATP Synthesis Driven by 
-Keto Acid-stimulated Alternative Oxidase in Pea Leaf Mitochondria
Department of Biology and Agro-Industrial Economics, Section of Plant Biology, University of Udine via Cotonificio 108, 1-33100 Udine, Italy
The electrical potential difference (
) generation and ATP synthesis due to 
-keto acid-stimulated alternative oxidase activity in pea leaf mitochondria, energized by malate plus glutamate, was studied. In the absence of -keto acids, was ca. 60% collapsed by KCN or antimycin A (AA), while the remaining part (ca. 30%) was dissipated by salicyl-hydroxamic acid (SHAM). The presence of -keto acids (pyruvate or iodoacetate), known to stimulate the alternative oxidase, caused a decrease in the KCN- or AA-sensitive component of (ca. 30%), which was accompanied by an increase in the SHAM-sensitive one. When mitochondria were energized by exogenous NADH, succinate or duroquinol, was completely collapsed by KCN or AA, either in the presence or absence of -keto acids. ADP partially collapsed the SHAM-sensitive component of , 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. ADP 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 -keto acids, stimulating the oxidation of NAD-linked substrates through the alternative oxidase, lead to an increase in the SHAM-sensitive component of via complex I, thus increasing the contribution of this pathway to ATP synthesis when the cyto-chrome oxidase is restricted.
(Received April 30, 1997; Accepted October 7, 1997)
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