Localization of fatty acid P-oxidation system in microbodies of Candida tropicalis cells growing on n-alkanes was studied. Microbodies isolated from the yeast cells showed palmitate-dependent activities of NAD reduction, acetyl-CoA formation and oxygen consumption. When sodium azide, an inhibitor of catalase, was added to the system, palmitate-dependent formation of hydrogen peroxide was observed. Stoichiometric study revealed that two moles of NAD were reduced per one mole of oxygen consumed in the absence of sodium azide and the presence of the inhibitor doubled the oxygen consumption by microbodies without an appreciable change in NAD reduction. These results indicate that the yeast microbodies contain P-oxidation system of fatty acid, and that catalase located in the organelles participates in the degradation of hydrogen peroxide to be formed at the step of dehydrogenation of acyl-CoA.Previous papers from our laboratory reported first on the profuse appearance of microbodies (peroxisomes) in the cells of various kinds of yeasts growing on n-alkanes [I -41. Similar phenomena were observed when higher fatty acids were used as carbon and energy source for these yeasts. Microbodies of n-alkane-grown cells of Candida tropicalis were isolated and localization of catalase, D-amino acid oxidase, isocitrate lyase, malate synthase and NADP-linked isocitrate dehydrogenase in the isolated microbodies was ascertained [5]. On the other hand, neither the components of n-alkane hydroxylation system, cytochrome P-450 and NADPH-cytochrome c reductase [6,7], nor enzymes of tricarboxylic acid cycle were contained in the organelles. The presence of isocitrate lyase and malate synthase suggested strongly that the organelles participate in the biosynthesis of C4-compounds from acetyl-CoA during n-alkane assimilation by the yeast.This paper describes localization of p-oxidation system in the microbodies of n-alkane-grown C. tropicalis. The results obtained indicate that the system of the yeast would be analogous to that found in microbodies of castor bean [8], rat liver [9], Tetralzyrnena [lo] and Euglena [ll]. Catalase was found to be linked to the P-oxidation system of the yeast,

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