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SUMMARY: 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. lipolytica 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 aa 3 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 obsered 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. lipolytica consisted mainly of equal amounts of oleic (C18:1) and linoleic (C18:2) unsaturated fatty acids, each making up about 40% of the total. In contrast, S. cerevisiae mitochondria contained palmitoleic (C16:1) (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 (C17:1) up to 75% when grown on odd-numbered n-alkanes of increasing carbon-chain length from C11 to C15. The changes in fatty-acid composition were correlated with changes in membrane fluidity as measured by differences in transition temperatures in Arrhenius plots of mitochordrial 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.