CHARACTERIZATION OF BETA-GALACTOSIDASE FROM SACCHAROMYCES FRAGILIS1

Abstract

Studies were made on physical and chemical characteristics of β-galactosidase in cell-free extracts of Saccharomyces fragilis Y-1109. The enzyme was stable at pH 6.0–7.0. When frozen in buffer solution, it was stable for more than 3 months but at 51 C, it lost 96% of the activity in 10 min. The optimum pH for lactose hydrolysis at 37 C was 6.5. The enzyme was activated by K+ while Mn++ served as the cofactor for the enzyme. Manganese appeared to be important in maintaining the integrity of the secondary and tertiary structure of the enzyme molecule. Inactivation of the enzyme by urea indicated the importance of secondary and tertiary structure in the enzymatic function of the yeast β-galactosidase. Beta-galactosidase appeared to be a sulfhydryl enzyme since heavy metals, p-chloromercuribenzoate, and iodoacetate inhibited the enzyme. Cysteine and galactose were competitive inhibitors of the enzyme, whereas glucose and various amines were non-competitive inhibitors.