IDENTITY OF BETA-GLUCOSIDASE AND BETA-XYLOSIDASE ACTIVITIES IN RAT LIVER LYSOSOMES

1. 1.|Subcellular distribution studies of rat liver β-glucosidase (β-d-glucosidase glucohydrolase, EC 3.2.1.21) and β-xylosidase (β-d-xyloside xylohydrolase, EC 3.2.1.37), using p-nitrophenyl-β-d-glucopyranoside and p-nitrophenyl-β-d-xylopyranoside as a substrate, respectively, show these enzyme activities to be localized in the lysosomes. The β-glucosidase to β-xylosidase ratio in all subcellular fractions is constant. 2. 2.|Both of the activities are more than 80% bound to the lysosomal membrane. 3. 3.|Maximum hydrolysis of p-nitrophenyl-β-d-glucopyranoside and p-nitrophenyl-β-d-xylopyranoside occurs at pH 5.2. The Km with p-nitrophenyl-β-d-glucopyranoside is I.45 mM and with p-nitrophenyl-β-d-xylopyranoside it is 4.05 mM. 4. 4.|Glucono-(I→4)-lactone, a specific competitive inhibitor of β-glucosidase, inhibited the hydrolysis of p-nitrophenyl-β-d-glucopyranoside and p-nitrophenyl-β-d-xylopyranoside with a Ki of 1.7 mM. p-Chloromercuribenzoate also inhibits both the activities with a Ki of 12.5 μM. 5. 5.|The pH stability of the two activities at 37, 50, and 60° is similar. 6. 6.|Both the activities are eluted from DEAE-cellulose by 0.122-0.155 M NaCl. 7. 7.|The results of these studies strongly support the conclusion that a single enzyme is responsible for both of the activities. © 1969.