SUMMARY: Mitochondria isolated from Tetrahymena pyriformis carried out oxidative phosphorylation with succinate and 2-oxoglutarate as substrates. Electron transport was inhibited by rotenone, piericidin A, antimycin A and cyanide. Succinate-cytochrome and ferricyanide oxidoreductases were antimycin A sensitive. NADH-cytochrome and ferricyanide oxidoreductases were only partially inhibited by high concentrations of rotenone. Externally added NADH gave no oxygen uptake in the absence of artificial electron acceptors. The mitochondria contained haems and protohaem, and difference spectra revealed the presence of cytochromes and a pigment with an extinction maximum at 620 nm. Steady-state and kinetic measurements of cytochrome components were made. Several kinetically distinct flavoprotein components were present. Kinetic measurements suggested that the reduced 620 nm. component reacted sufficiently rapidly with molecular oxygen to have been the terminal oxidase.


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