PURIFICATION AND PROPERTIES OF AN INDUCIBLE β-GLUCOSIDASE OF BAKERS' YEAST

Abstract

The inducible β-glucosidase present in crude extracts of cellobiose-grown bakers' yeast (Saccharomyces cerevisiae C) was purified 50-fold and found to be homogeneous in the ultracentrifuge, with a molecular weight of 313,000. The enzyme was virtually identical in its properties with the internal, cryptic enzyme of the yeast cell, revealed by butanol treatment of the suspensions. It was unlike the membrane-localized enzyme found at the surface of intact cells in its low affinity for cellobiose and methyl-β-glucoside as substrates and inhibitors. The enzyme was specific for the β configuration and had no activity against substrates such as α-glucosides, β-galactosides, or β-xylosides. It was highly active against both naturally occurring and synthetic substrates with aromatic aglycones, and may thus be classed as an aryl-β-glucosidase. The enzyme had weak hydrolytic activity against methyl-β-glucoside and cellobiose, but these compounds, unlike all of the aryl-β-glucosides tested, were not competitive inhibitors of its activity against the chromogenic substrate pNPG. There were about 40,000 molecules of enzyme per cell in fully induced cultures and the enzyme represented about 3% of the total protein of these cells.