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Articles

Cyanide-resistant Respiration of Sweet Potato Mitochondria ¹

^a Southern Region, Agricultural Research Service, United States Department of Agriculture, Departments of Botany and Crop Science, North Carolina State University, Raleigh, North Carolina 27607

The oxidation of malate and succinate by sweet potato mitochondria (Ipomoea batatas [L.] Lam.) was blocked only partly by inhibitors of complexes III (2-heptyl-4-hydroxyquinoline-N-oxide) and IV (cyanide and azide). The respiration insensitive to inhibitors of complexes III and IV was inhibited by salicylhydroxamic acid. Essentially complete inhibition was obtained with inhibitors of complex I (rotenone, amytal, and thenoyltrifluoroacetone) and complex II (thenoyltrifluoroacetone). The observations indicated that electrons were transferred to the cyanide-resistant pathway from ubiquinone or from nonheme iron (iron-sulfur) proteins of complexes I and II before reaching the b cytochromes. In contrast, the oxidation of exogenous NADH did not involve the alternate pathway, as indicated by complete inhibition by inhibitors of complexes III and IV and the absence of an effect of inhibitors of complexes I and II. Hence, electrons from exogenous NADH appear to pass directly to complex III in sweet potato mitochondria.

¹ This research is the result of cooperative investigations of the North Carolina Agricultural Experiment Station and the Southern Region, Agricultural Research Service, United States Department of Agriculture, Raleigh, N. C. Paper No. 4428 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, N. C. These investigations were supported in part by Public Health Service Grants ES 00044 and ES 00083. These investigations were reported in a thesis submitted by P.F.T. in partial fulfillment of the requirements for the M.S. degree, Department of Botany, North Carolina State University, Raleigh, N. C. 1974.