β-Glucosidase and β-xylosidase of rat kidney

Abstract

1. 1.|Subcellular distribution studies of rat kidney β-glucosidase ( β- d - glucoside glucohydrolase, EC 3.2.1.21), β-xylosidase ( β- d - xyloside xylohydrolase , EC 3.2.1.37) and β-galactosidase (β- d-galactoside galactohydrolase EC 3.2.1.23) using p-nitrophenol derivative substrates show β-glucosidase and β-galactosidase to be localized in lysosomes and the supernatant fraction. β-Xylosidase activity is mainly localized in lysosomes, however, the supernatant fraction has significant activity. 2. 2.|Lysosomal β-glucosidase and β-xylosidase are tightly bound to the membrane, whereas β-galactosidase is easily solubilized by a free-thaw treatment. 3. 3.|Lysosomal β-glucosidase and β-xylosidase have optimum activity at pH 5.0. The supernatant β-glucosidase and β-xylosidase have optimum activity at pH 6.4 and 5.2, respectively. The supernatant β-galactosidase has two pH optima, 2.2–3.4 and 3.6–4.8. 4. 4.|Glucono(1→4)lactone inhibits the hydrolysis of p- nitrophenyl-β- d-glucopyranoside and p- nitrophenyl-β- d-xylopyranoside ; β-galactosidase activity is inhibited at pH 6.6 but not at pH 3.4. p-Chloromercuribenzoate inhibits all three activities. 5. 5.|The pH stabilities of lysosomal β-glucosidase and β-xylosidase activities at 37° are similar. 6. 6.|Lysosomal β-glucosidase and β-xylosidase have the same elution pattern from a DEAE-cellulose column, as does the supernatant β-glucosidase, β-xylosidase and β-galactosidase (pH 6.6). 7. 7.|The results of these studies strongly support the conclusion that a single enzyme is responsible for both β-glucosidase and β-xylosidase activity in lysosomes. β-Glucosidase and β-xylosidase, and probably β-galactosidase (pH 6.6), activities in the supernatant fraction are exhibited by a single enzyme.