Lactose Utilization and Hydrolysis in Saccharomyces fragilis

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Abstract
Summary: Sodium azide, 2,4-dinitrophenol and iodoacetate did not inhibit hydrolysis of lactose by cell-free preparations of Saccharomyces fragilis β-galactosidase, but with intact organisms fermentation and hydrolysis were inhibited to a similar extent. This suggests that these inhibitors may interfere with the transport of lactose into the cell. Galactose fermentation was inhibited by sodium azide and dinitrophenol to a much greater extent than was glucose or lactose fermentation. Hydrolysis of lactose and o-nitrophenyl-β-d-galactoside required potassium ion at an optimal concentration of 0·1M; ammonium ion also activated, but sodium ion was much less effective and, in presence of optimal concentrations of potassium ion, were inhibitory, as were calcium and zinc ions. Lithium, magnesium and manganese ions were without effect in presence of potassium optimal ion. The β-galactosidase activity of aqueous suspensions of acetone-dried organisms, or of cell-free extracts, decayed rapidly at 25°. This decay was prevented by addition of sodium phosphate or various potassium salts, but not by sodium or potassium chloride or by potassium sulphate. Sodium azide, arsenate or 2,4-dinitrophenol decreased the rate of decay and promoted partial recovery when decayed preparations were subsequently incubated with potassium phosphate. The enzyme was most stable in 0·1m-potassium phosphate (pH 7·0). A purified (237-fold) preparation of the β-galactosidase was obtained; this too decayed rapidly in water or potassium chloride solution but not in potassium phosphate solution.