Enzymic activity of the K5-type yeast killer toxin and its characterization

Abstract

K5-type yeast killer toxin secreted by P. anomala NCYC 434 cells has a broad killing spectrum. Competitive inhibiton of killer activity showed that glucans, mainly the β-1,3 glucan, represent the primary toxin binding site within the cell wall of sensitive cells. Its hydrolytic activity on laminarin in an exo-like fashion revealed that the toxin exerts its killing effect by exo-β-1,3-glucanase activity. Its specific activity on laminarin was 120 U/mg, and the Michaelis constants Km and Vmax for laminarin hydrolysis were 0.25 mg/ml and 370 μmol/min/mg. The toxin exerted its cytocidal effect after 2 h contact with the target cells. Production of the toxin by the cells was induced only when they were grown in culture media rich in β-glucan sources, and the addition of glucose increased the specific production rate. The enzymic activity of the toxin was fully inhibited by Hg+2, but increased with some other metal ions, most of all by Pb+2.