RAT-LIVER LYSOSOMAL BETA-GLUCOSIDASE - A MEMBRANE ENZYME

1. 1.Intracellular distribution studies of rat-liver β-glucosidase (β-d-glucoside glucohydrolase, EC 3.2.1.21), using p-nitrophenyl-β-d-glucopyranoside as substrate, show it to be localized in the lysosomal fraction. 2. 2.The enzyme is well resolved from β-galactosidase (EC 3.2.1.23) and other lysosomal enzymes, due to its retention on the membrane. The action of β-galactosidase with pH optimum of 3.0 is demonstrated upon lactose and both o- and p-nitrophenyl substrates. β-Glucosidase is also distinguished from β-acetylglucosaminidase (EC 3.2.1.30), another membrane enzyme. 3. 3.β-Glucosidase has maximum activity at pH 5.0 and a Km (app) of 0.17 mM p-nitrophenyl-β-d-glucopyranoside. The activity is linear with protein and linear with time for at least 60 min. 4. 4.Activity upon p-nitrophenyl-β-d-xylopyranoside is also found in the lysosomal membrane fraction. 5. 5.The significance of enzyme binding to the membrane is discussed. © 1968.