SUMMARY: A method for determining the lactase activity of is described. The yeast is treated with cetyltrimethylammonium bromide, and the products of lactose hydrolysis are fermented with . The formation of lactase in was studied by using the continuous culture technique. Lactase formation was inhibited by the presence of sugars in the medium at concentrations greater than 0·001% (w/v), but the magnitude of the inhibition and the range of activity over which it occurred depended on the nature of the sugar in the medium. With media containing glucose or sucrose, activities up to 10 units lactase/mg. dry weight were found when the sugar concentration was less than 0·001% (w/v), while at high concentrations lactase activity was almost completely absent. With media containing galactose or lactose at concentrations less than 0·001% (w/v) activities of approximately 100 units lactase/mg. dry weight were observed, while at concentrations greater than 0·01% (w/v) the activity was less. The mean generation time of the organisms and the concentrations of growth factors, ammonium and hydrogen ions had, over the range tested, no significant effect on lactase formation. The lactase activity found in intact organisms was always lower than the activity found in disrupted organisms, irrespective of the conditions under which the yeast had been grown. Possible interpretations of this phenomenon are discussed.


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