Purification and characterization of extracellular and intracellular killer toxin of Saccharomyces cerevisiae strain 28

Institut fur Mikrobiologie und Weinforschung der Johannes Gutenberg-Universität Mainz, Postfach 3980, D-6500 Mainz, Federal Republic of Germany ABSTRACT SUMMARY: The extracellular killer toxin of Saccharomyces cerevisiae strain 28 was concentrated by ultrafiltration of culture supernatants and purified by ion-exchange chromatography. Polyacrylamide gradient gel electrophoresis in SDS indicated that the toxin is a glycoprotein with a molecular weight of about 16000. Amino acid analysis revealed that the killer toxin contains 111 amino acid residues, equivalent to a molecular weight of 14045; the ratio of protein to carbohydrate in the molecule is therefore about 9 to 1. The isoelectric point of the killer toxin was pH 4.4 to 4.5. The toxin was unaffected by heating at 40 °C for 1 h and its maximum activity against sensitive yeast cells was observed at pH 5.0. Cell-free extracts prepared from well-washed cells of S. cerevisiae strain 28 were toxic for sensitive yeasts. The toxin present in these extracts (intracellular toxin) was partially purified by ultrafiltration and ion-exchange chromatography. The isoelectric points of the extracellular and intracellular killer toxin were similar.