Two exopolyphosphatases of the cytosol of the yeast S. cerevisiae: comparative characteristics.

In cell-free extracts of the yeast Saccharomyces cerevisiae that had been transferred from phosphate-deficient (-P) medium to complete (+P) medium ("hypercompensation" conditions), the specific and the total polyphosphatase activities increased (by 50 and 60%, respectively) compared to the control that was transferred from (+P) medium to (+P) medium. Specific and total polyphosphatase activities under "hypercompensation" conditions increased by 25 and 43% in cytosol, by 33 and 100% in vacuoles, and by 50 and 50% in the total membrane fraction, respectively. In contrast, the polyphosphatase activity in the cell envelope somewhat decreased compared to the control. Under the growth conditions indicated above, a novel high molecular weight polyphosphatase was revealed in the cytosol fraction along with the previously studied 40-kD polyphosphatase. Unlike the 40-kD polyphosphatase, which is most active with tripolyphosphate, this novel enzyme has a molecular mass of more than 440 kD and is most active with high molecular weight polyphosphates. This polyphosphatase is insensitive to antibodies that suppress the activity of the 40-kD polyphosphatase of the cytosol. In a number of properties, the high molecular weight polyphosphatase of the cytosol resembles the polyphosphatase of vacuoles, but it differs from the polyphosphatases of nuclei and mitochondria of S. cerevisiae. The ratio of the low and high molecular weight polyphosphatases depends on the culture growth conditions. Under "hypercompensation" conditions, the total activity of the high molecular weight polyphosphatase in the cytosol is five times higher than that of the 40-kD polyphosphatase. During growth without re-inoculation, the 40-kD polyphosphatase is predominant in the cytosol; its total activity in dependence on the growth stage is 3.5-12.5 times higher than the activity of the high molecular weight form.