Biosynthesis of acid phosphatase of baker's yeast . Characterization of a protoplast-bound fraction containing precursors of the exo-enzyme

Abstract

1. 1.|Yest protoplasts, secreting acid phosphatase (orthophosphoric-monoester phosphohydrolase (acid optimum) EC 3.1.3.2) contain a small amount of firmly bound enzyme, even after lysis (Van Rijn, H.J.M.; Boer, P. and Steyn-Parvé, E.P. (1972) Biochim. Biophys. Acta 268, 431–441). The major part (70%) of this protoplast-bound acid phosphatase can be solubilized by non-ionic detergents, such as Triton X-100.

2. 2.|The kinetics of radioactive amino acid incorporation in the solubilized and in the secreted enzyme has been estimated by pulse-chase labelling of secreting protoplasts, followed by fractionation and counting radioactivity in the enzyme band in polyacrylamide gels after electrophoresis at pH 5.0. A precursor-product relationship between the Triton X-100-extractable fraction of the protoplast-bound acid phosphatase and the secreted enzyme is apparent.

3. 3.|The solubilized acid phosphatase is essentially indistinguishable from the secreted enzyme with regard to a number of enzymatic properties and its stability towards pH and temperature. Both enzymes also behave alike on polyacrylamide-gel electrophoresis, producing a single acid phosphatase band with glycoprotein character and comparable mobility.

4. 4.|A striking difference is seen in isopycnic equilibrium sedimentation in CsCl: the secreted acid phosphatase is homogeneous, with a buoyant density of π = 1.47 g/cm3, while the Triton X-100-extractable part of the protoplast-bound acid phosphatase is heterogeneous; besides heavier