Expulsion of uracil and thymine from the yeast Saccharomyces cerevisiae: contrasting responses to changes in the proton electrochemical gradient

Article Abstract:

The changes in the proton electrochemical gradient (delta-mu-minus-(sub H+)) was measured to define its role in uracil and thymine efflux in Saccharomyces cerevisiae. It was found that the delta-mu-minus-sub H+ has no effect on uracil transport in yeast preparations where ATP levels have been depleted, indicating that the efflux of uracil appears not to be driven by proton gradient. Instead, it may directly use ATP. Thymine uptake in the absence of glucose or after the depletion of ATP occurred when the delta-mu-minus-sub H+ was used up either by DNP or azide or by manipulation of the external environment. The absorbed thymine was found to be expelled when the delta-mu-minus-sub H+ was brought back to physiological range.

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Demonstration of high-affinity Mn2+ uptake in Saccharomyces cerevisiae: specificity and kinetics

Article Abstract:

Saccharomyces cerevisiae has a high-affinity Mn2+/H+ antiport system for Mn2+ transport at low Mn2+ concentrations and a low-affinity transport system at high Mn2+ concentrations. The high-affinity system has a K(sub m) of 0.3 micro-M and is competitively suppressed by ions such as Mg2+ and Zn2+. The low-affinity system has a K(sub m) of 62 micro-M and is non-competitively suppressed by Mg2+. The low-affinity system is more specific for Mn2+ ions than the high-affinity system. The transport of Mn2+ in the presence of toxic concentrations of Mn2+ has a negative value of K(sub m).

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Cytosine accumulation as a measure of the proton electrochemical gradient acting on the overexpressed cytosine permease of Saccharomyces cerevisiae

Article Abstract:

Previous research has failed to determine the magnitude of the proton electrochemical gradient that drives the accumulation of diverse nutrients in Saccharomyces cerevisiae. This can be attributed to the lack of a suitable assaying technique for its electrical component, the membrane potential. To remedy this problem, the steady-state of cytosine distribution established by a strain of Saccharomyces cerevisiae is studied to assay its proton and pH gradients, thus allowing the assaying of the membrane potential.

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