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 oligosaccharide containing 8-11 glucose residues has been formed. Although glycogenin, under physiological conditions, is both enzyme and acceptor in the glucosyl transfer reactions, it is also capable of utilizing p-nitrophenyl-linked malto-oligosaccharides as exogenous acceptors. In view of the potential usefulness of exogenous acceptors in the study of the mechanism of the glycogenin reaction, we have expanded the search for such compounds and report here that several alkyl glucosides and alkyl maltosides may serve as acceptors in glucosyl transfer by beef kidney glycogenin. Dodecyl-beta-D-maltoside (Km approximately 100 microM) was the most effective acceptor among the compounds tested and yielded 30 times as much product as p-nitrophenyl-alpha-maltoside. Substantial product formation was also observed with tetradecyl-beta-D-maltoside and octyl-beta-D-maltoside (39 and 22%, respectively, of the value measured for dodecyl-beta-D-maltoside). It was further demonstrated that dodecyl-beta-D-maltoside served as an acceptor in the transfer of xylose from UDP-xylose, indicating that the exogenous substrate behaved similarly 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 active in vivo and in cell culture as artificial initiators of glycogen synthesis.