Change in transport activities of vacuoles of the yeast Yarrowia lipolytica during its growth on glucose.

Vacuoles were isolated from Yarrowia lipolytica yeast cells taken at various growth phases under carbon or nitrogen limitation. Vacuoles from the cells at the logarithmic growth phase showed a high activity of vacuolar H(+)-ATPase (0.9-1.1 U/mg protein) and efficiently generated chemical proton gradient and membrane potential across the tonoplast. Ca(2+)- and citrate transport were found to be maximal at this growth phase. At growth retardation and then in the stationary phase all the parameters studied decreased irrespective of the method of growth limitation. The citrate-transporting activity of vacuoles completely disappeared at growth retardation, also irrespective of the limitation method and irrespective of whether yeast cells overproduced citrate in the culture medium. The citrate-transporting system of Y. lipolytica vacuolar membrane is concluded not to be involved in citrate efflux and this efflux is probably performed by the plasmalemma transport system.

Effect of oxygen limitation on the content of n-hexadecane-inducible cytochrome P-450 in Acinetobacter calcoaceticus strain EB 104.

The content of cytochrome P-450 as a function of oxygen supply was studied during growth of Acinetobacter on n-hexadecane in batch cultures at constant pH and agitation. The rate of growth and the content of cytochrome P-450 were not affected as long as the dissolved oxygen tension ranged above 3 to 5% of saturation. The amount of cytochrome P-450 increased when the oxygen tension declined to zero. Cytochrome P-450 levels of about 0.3 to 0.4 nmol/mg protein, i.e. a more than a threefold increase, were observed under conditions where oxygen supply was strictly limited and allowed to maintain only a minimum of metabolism or growth. Limited oxygen supply exerted a special effect on the induction of the cytochrome P-450 as concluded from an increasing ratio between cytochrome P-450 and cytochrome o, and from the absence of cytochrome d in cells with elevated content of cytochrome P-450. The increased formation of cytochrome P-450 was a reversible process.