The properties of cells and mitochondria isolated from Candida lipolytica, a hydrocarbon-utilizing yeast, grown on ethanol, glucose and n-alkanes were examined. A comparative study was made of the properties of the whole cells and mitochondria of C. ZipoZytica and of those of Saccharomyces cerevisiae.The reduced-minus-oxidized cytochrome spectrum of C. lipolytica grown on ethanol showed a much larger amount of cytochromes aa3 and a very broad cytochrome b-type absorption band compared with S. cerevisiae. The relative amounts of cytochromes in C . lipolytica on hydrocarbons differed according to the growth phase but never reached the levels observed in the cells grown on ethanol. Furthermore, as judged by the reduced-minus-oxidized cytochrome spectra, C. lipolytica was much less affected by glucose repression than was S. cerevisiae. The fatty acids of mitochondria isolated from ethanol-grown C. l@oZytica consisted mainly of equal amounts of oleic (CI8J and linoleic (C1,:2) unsaturated fatty acids, each making up about 40 % of the total. In contrast, S. cerevisiae mitochondria contained palmitoleic (ClGZl) (approx. 45 %) and oleic (approx. 35 %) as the main fatty-acid components. There was an increase in the amount of oleic acid (60 %) relative to linoleic acid (20 %) when C. lipolytica was grown on even-numbered hydrocarbons and a progressive increase in the amount of heptadecenoic acid (C1,:,) up to 75 % when grown on odd-numbered n-alkanes of increasing carbonchain length from C,, to CI5. The changes in fatty-acid composition were correlated with changes in membrane fluidity as measured by differences in transition temperatures in Arrhenius plots of mitochondria1 membrane-bound enzymes.The ATPases of C. lipolytica and S. cerevisiae mitochondria were examined, and marked differences in specific activity (3-to 5-fold higher in S. cerevisiae), pH profile and oligomycin sensitivity were noted.

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Workers in several laboratories have recently reported the isolation of respiratorycompetent oligomycin-resistant mutants of Saccharomyces (Stuart, 1970; Wakabayashi & Gunge, 1970; Avner & Griffiths, 1970). We have further subdivided these mutants into two phenotypic classes on the basis of their cross-resistance to a range of inhibitors and uncouplers of mitochondrial energy-linked reactions (Avner & Griffiths, 1973a,b). Although the ATPase" activities of mitochondria from the oligomycin-resistant mutants are more resistant to inhibition by oligomycin than those of the corresponding enzyme of the parent strain (Griffiths et al., 1972), the exact nature of the lesion is as yet unclear. Previous work on yeast mitochondrial ATPase has almost exclusively been confined to studies on Saccharomyces yeast (Schatz, 1968; Kovac et al., 1968; Somlo, 1968). In the present work we have examined and compared the properties of the ATPase of mitochondria from Saccharomyces cerevisiae and Candida lipolytica. We chose to examine C. lipolytica mitochondrial ATPase because in several other properties, such as cytochrome content and unsaturated fatty acid composition (Skipton et al., 1973), these mitochondria are quite different from those of mitochondria from S. cerevisiae. The yeast strains C. lipolytica YB423 (B.P. Chemicals, Gpernon, France) and S. cerevisiae D22 were grown aerobically at 30°C in New Brunswick Fermentors in a medium containing 1 % yeast extract, 0.2% peptone, mineral salts (Wickerham, 1946) and 0.5 % ethanol as C source. Cells were harvested at the end of the exponential phase