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Metabolism and Enzymology

Modulation of the Access of Exogenous NAD(P)H to the Alternative Pathway in Potato Tuber Callus Mitochondria with Triton X-100

Department of Physiology and Biochemistry of Plants, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands

Alternative oxidase activity in potato tuber (Solanum tuberosum L. cv Bintje) callus mitochondria with exogenous NAD(P)H as substrate is inhibited by low concentrations of the detergent Triton X-100. Alternative oxidase activity with succinate or malate as substrate is not affected by these low concentrations of Triton X-100. Cytochrome pathway activity was not influenced under these conditions, neither with endogenous nor with exogenous substrate. Washing of Triton X-100-treated mitochondria did partially restore both uninhibited and CN-resistant NADH oxidation, indicating that under these conditions Triton X-100 does not permanently remove major components from the mitochondrial membrane. Apparently, it is possible to manipulate mitochondria in such a way that the access of exogenous NADH to the alternative pathway is blocked while access to the cytochrome pathway is uninhibited. It is suggested that membrane conditions have a regulatory function (possibly via influencing the diffusion path) in the oxidation of exogenous NADH via the alternative pathway.