DODECYL-BETA-D-MALTOSIDE AS A SUBSTRATE FOR GLUCOSYL AND XYLOSYL TRANSFER BY GLYCOGENIN

Glycogenin is the core protein of glycogen proteoglycan and is, at the same time, a self-glucosylating enzyme which catalyses early glucosyl transfer steps in the biosynthesis of glycogen, In the course of this process, glycogenin is glucosylated progressively until an oligosacch aride containing 8-11 glucose residues has been formed, Although glyco genin, under physiological conditions, is both enzyme and accepter in the glucosyl transfer reactions, it is also capable of utilizing p-nit rophenyl-linked malto-oligosaccharides as exogenous accepters. In view of the potential usefulness of exogenous accepters in the study of th e mechanism of the glycogenin reaction, we have expanded the search fo r such compounds and report here that several alkyl glucosides and alk yl maltosides may serve as accepters in glucosyl transfer by beef kidn ey glycogenin. Dodecyl-beta-D-maltoside (K-m similar to 100 mu M) was the most effective acceptor among the compounds tested and yielded 30 times as much product as p-nitrophenyl-alpha-maltoside. Substantial pr oduct formation was also observed with tetradecyl-beta-D-maltoside and octyl-beta-D-maltoside (39 and 22%, respectively, of the value measur ed for dodecyl-beta-D-maltoside). It was further demonstrated that dod ecyl-beta-D-maltoside served as an acceptor in the transfer of xylose from UDP-xylose, indicating that the exogenous substrate behaved simil arly to glycogenin itself in this regard, Dodecyl-beta-D-maltoside has already proven useful in the development of a simple glycogenin assay , and it is further suggested that this and related compounds may be a ctive in vivo and in cell culture as artificial initiators of glycogen synthesis.