Zymolyase, produced by a submerged culture of Arthrobacter luteus, is an enzyme preparation which effectively lyses cell walls of viable yeast cells. An essential enzyme responsible for lysis of viable yeast cell walls in this preparation is b-1,3-glucan laminaripentaohydrolase. It hydrolyzes linear glucose polymers with b-1,3-linkages and releases specifically laminaripentaose specifically as the main and minimum product unit. This lytic activity releases spheroplasts and protoplasts in the preparation of yeast DNA prior to restriction enzyme digestion and Southern Blot analysis. The extent of lysis of yeast cells by Zymolyase varies with yeast strain, growth stage of yeast and cultural condition.