Properties of fructose-1,6-bisphosphate aldolase inactivating enzymes in rat liver lysosomes.

The intralysosomal localization of the enzymes that catalyse inactivation of rat liver fructose-bisphosphate aldolase (D-fructose-1,6-bisphosphate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13) to a form with antigenic activity was demonstrated. The inactivating enzymes like all other lysosomal markers tested except acid phosphatase, were readily solubilized by hypotonic shock. The inactivating enzyme activity was inhibited by PMSF, TPCK, TLCK and leupeptin, but not by pepstatin. On partial purification of the inactivating activity from the lysosomal fraction by DEAE-Sephadex (A-50) and Sephadex G-100 column chromatographies, it was copurified with lysosomal carboxypeptidase A and cathepsin B (EC 3.4.22.1). Studies on its substrate specificity and sensitivity to inhibitors indicated that cathepsin B and carboxypeptidase A are responsible for almost all the aldolase-inactivating activity in the lysosomal fraction.