THE CONTENT OF ALTERNATIVE OXIDASE OF EUGLENA MITOCHONDRIA IS INCREASED BY GROWTH IN THE PRESENCE OF CYANIDE AND IS NOT CYTOCHROME O

A study of the effect of respiratory inhibitors on O-2 uptake of Eugle na gracilis mitochondria, isolated from cells grown in the presence of cyanide or with ethanol as carbon source, was undertaken. The content s of cytochrome c oxidase and alternative oxidase were also determined . Inhibition of respiration by antimycin and cyanide was only partial and it was dependent on the oxidizable substrate used. Succinate oxida tion was the most sensitive to cyanide whereas lactate oxidation was t he most resistant. Cell growth in the presence of cyanide or with etha nol as carbon source brought about an enhanced content of alternative oxidase without a concomitant increase in cytochrome aa(3) content. Ho wever, a correlation between cyanide-resistant respiration and alterna tive oxidase content was not found. Analysis of heme types in mitochon drial membranes revealed the absence of heme O. The data suggest the p resence of an inducible alternative oxidase in Euglena mitochondria wh ich has high resistance to cyanide and contains heme B. A close relati onship between Euglena alternative oxidase and bacterial quinol oxidas es containing B-type heme is proposed.