Concerted action of beta-glucuronidase and beta-acetylglucosaminidase on hyaluronodextrins

Abstract

A kinetic analysis of the stepwise alternating action of beta-glucuronidase and beta-acetylglucosaminidase on oligosaccharides and dextrins derived from hyaluronic acid was undertaken, for better definition of the contribution of this process to hyaluronate catabolism. Production of monosaccharide from larger dextrins by action of either enzyme is powerfully inhibited by electrolyts. In the study, as in mammalian tissues, beta-glucuronidase is present in excess so that the concentration of beta-acetylglucosaminidase is rate controlling in the action on dextrin substrates. For this action, Vmax shows limited variation with ionic strength or molecular weight of substrate. At ionic strength 0.03, but not 0.18, Km decreases some 100-fold for increase of molecular weight from 2,000 to 15,000. It is specifically this decrease in Km that accounts for the prominent electrolyte inhibition observed with larger dextrins. The extremely low values of Km are attributed to multiple ionic enzyme-substrate interactions at sites remote from the catalytic center. The previously reported stimulation by electrolyte of the action of beta-glucuronidase and beta-acetylglucosaminidase on aryl glycosides, studied briefly, is apparently unrelated to the electrolyte effects seen with dextrins. The catabolic contribution of beta-glucuronidase and beta-acetylglucosaminidase appears to be restricted to hydrolysis of the smaller oligosaccharides produced by action of hyaluronidase, since, for any reasonable assumptions regarding cellular environment, the extent of their action on polymeric hyaluronate or larger dextrins must be limited.