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An extracellular multiple form of endoxylanase was isolated from the xylanolytic complex of Aspergillus niger B03. Th e enzyme was purifi ed to a homogenous form using ultrafi ltration, anion exchange chromatography, and gel fi ltration. It was a nonglycosylated protein with a molecular weight of 20,000 Da as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 21,000 Da as determined by gel fi ltration. Th e optimal pH for the enzyme action was 5.0 and the optimal temperature was 55 °C. Endoxylanase stability was signifi cantly improved in the presence of glycerol and sorbitol. Th e enzyme activity was activated by Mn 2+ and Co 2+ , and it was inhibited by Ag + , Cu 2+ , Fe 3+ , Fe 2+ , and Pb 2+ . Th e substrate specifi city and the product profi le of the enzyme suggested that it was an endoxylanase. Th e enzyme showed a synergism with another endoxylanase from Aspergillus niger B03 in xylan hydrolysis.

A series of prototrophic fragile strains of different ploidy (2n, 3n and 4n) has been genetically constructed on the basis of haploid srb1 containing segregants of the fragile Saccharomyces cerevisiae mutant VY 1160. The strains have been characterized by several criteria. In regard to generation time, biomass yield, and nucleic acids content of the cells, the tetraploid srb1 homozygous hybrid is indistinguishable from an industrial strain of S. cerevisiae. However, it is characterized by a higher protein content. Unlike any other laboratory or industrial strains, the original mutant and these hybrids possess an ability for lysis upon suspension in hypotonic solutions. The dependence of the percentage of lysed cells on the growth phase and concentration of osmotic stabilizer in the medium has been investigated. The quantity of proteins in the soluble and insoluble fractions obtained after lysis of these strains by osmotic shock has been determined. These hybrids can be considered as a potential industrial source of proteins for nutritional purposes.