Characterization of the Saccharomyces cerevisiae Y500-4L killer toxin

The strain Saccharomyces cerevisiae Y500-4L, selected from the must of alco hol producing plants, liberates a toxin which is lethal to the commercial y east produced by Fleischmann Royal Nabisco and other strains of yeast. This toxin was characterized, and the maximum production was obtained after 24 hours of incubation at 25 degreesC in YEPD medium. The maximum activity was achieved between pH 4.1 and 4.5 and between 22 and 25 degreesC and maximum stability in the pH range 3.8 to 4.5 at -10 degreesC. The killer toxin was inactivated by heating at 40 degreesC for 1 hour at pH 4.1. After concentr ation by ultrafiltration of culture supernatants and purification by gel fi ltration chromatography, the molecular weight of the purified toxin was est imated by SDS-PAGE to be about 18-20 kDa.