Studies on the αL-iduronidase activity of β-glucuronidase preparations from bovine liver, rat liver, and rat preputial gland

A commercial preparation of bovine liver β-glucuronidase contained two distinct enzyme species, both of which catalyze the hydrolysis of 4-methylumbelliferyl α-L-iduronide. The species with a molecular weight of about 290,000 was devoid of phenyl α-L-iduronidase activity and exhibited 4-methylumbelliferyl β-D-glucuronidase activity. The species with a molecular weight of about 78,000 was active towards phenyl α-L-iduronide but lacked the latter activity. Studies of the kinetics of inhibition and heat inactivation suggested that the hydrolysis of 4-methylumbelliferyl α-L-iduronide is due to the β-glucuronidase in the case of the 290,000-dalton species. The highly purified β-glucuronidase preparations derived from rat preputial gland and liver lysosomes also exhibited 4-methylumbelliferyl α-L-iduronidase activity. These findings support the view that β-glucuronidase can hydrolyze certain α-L-iduronide bonds and raise the possibility that β-glucuronidase may play a role in the catabolism of iduronic acid-containing glycosaminoglycans.