A strain of bakers' yeast was isolated which could utilize cellobiose and other ß-D-glucosides quantitatively as carbon and energy sources for growth. Cellobiose-grown cells contained a largely cryptic enzyme active against the chromogenic substrate p-nitrophenyl-ß-D-glucoside. The patent (intact cell) activity of such cells was inhibited by azide and, competitively, by cellobiose; neither agent inhibited the ß-glucosidase activity of lysed cells or of extracts. The enzyme induced by growth in cellobiose medium had no affinity for cellobiose as either substrate or inhibitor; its substrate specificity classifies it as an aryl-ß-glucosidase. It was concluded that growth in cellobiose also induced the formation of a stereospecific and energy-dependent system whose function determined the rate at which intact cells could hydrolyze substrates of the intracellular ß-glucosidase.

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