Ultracytochemical characterization of non-specific acid phosphatase activities in Saccharomyces cerevisiae.

Glutaraldehyde prefixation causes a considerable inactivation of the acid phosphatase of yeast protoplasts in dependence on the duration of aldehyde influence. Lead ions necessary for ultracytochemical demonstration effect a still stronger inhibition of enzymatic activity. Prefixation, however, protects the enzyme from further inhibition by lead. At pH 4.4 in intact cells acid phosphatase activities are mainly localized in the periplasmic space and in vesicles fused with the plasma membrane. The cell wall and cytoplasm usually remain free of reaction products. On the cell surface activities are found in form of globular lead deposits. At pH 5.2 and 6.3 the periplasmic activity appears decreased compared to that at lower pH values and the intracellular activity is increased. The plasma membrane of protoplasts is completely free of precipitates. The intracellular activity sites of protoplasts (cisternae of endoplasmic reticulum and/or Golgi-like system, small vesicles, central vacuole, nuclear envelope) are the same as for intact cells. The occurrence of at least two forms of acid phosphatase in S. cerevisiae id deduced.