Purification and Properties of the Killer Toxin Produced by a Halotolerant Yeast, Pichia farinosa

Abstract

The killer toxin produced by the Pichia farinosa KKl strain was purified by ammonium sulfate precipitation, gel filtration, ion-exchange chromatography and reverse-phase HPLC. The molecular weight of the killer toxin was about 25 kd and its isoelectric point was 6.4. A significant amount of carbohydrate was not detected in the purified killer toxin, suggesting that the toxin is not glycosylated. Its N-terininal amino acid sequence showed no homology with other proteins. The stability and efficacy of the toxin's killer activity was examined. The toxin completely retained activity at pH 2.5-4.0 and 5°C, but lost activity at higher temperatures. Killer activity increased with increasing NaCl or KCl concentration, although NaCl was more effective than KCl.