The effect of myo-inositol deficiency on phosphatases of yeast

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Abstract
Activities of several phosphohydrolases are significantly enhanced when cells of the inositol-requiring yeast, Saccharomyces uvarum ATCC 9080, are deprived of inositol. This effect is most pronounced for the external acid phosphatase [EC 3.1.3.2] and cannot be explained simply by limitation of cellular growth, because starvation for vitamins or sulfate has no effect on acid phosphatase activities. Excessive secretion of acid phosphatase by spheroplasts prepared from inositol-deficient cells is greatly reduced when the spheroplast medium is supplemented with inositol and is immediately suppressed by the addition of cycloheximide. These results together with data obtained from experiments with whole cells, employing cycloheximide and actinomycin D, point to a regulatory effect of inositol limitation at the level of transcription. The external enzymes .beta.-D-fructofuranosidase [EC 3.2.1.26], .alpha.-D-galactosidase [EC 3.2.1.22] and L-asparaginase, and the vacuolar enyzme carboxypeptidase Y [EC 3.4.16.1] are not affected by inositol deficiency, indicating that inositol deficiency has no general effect on protein secretion. [S. cerevisiae was also studied.].

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