We have described the purification of rabbit muscle proteoglycogen. Mild digestion of the purified proteoglycogen with ¦Á-amylase led us to prepare PG-200, a proteoglycogen species having a polysaccharide moiety of lower size than the native species (Carrizo, M.E., Miozzo, M.C., Goldraij, A., and Curtino, J.A. (1997) Glycobiology 7, 571-578). The polysaccharide bound glycogenin of PG-200 showed increased activation energy and lower catalytic activity for transglucosylation of DBM than polysaccharide-free glycogenin (Romero, J.M., Carrizo, M.E., Montich, G. and Curtino, J.A. (2001) Biochem. Biophys. Res. Commun., 289, 69-74). We now describe the ability of PG-200 for autoglucosylation when incubated with UDP-14C-glucose. During the incubation some polysaccharide-free glycogenin was released form PG-200 due to a slight contamination of the PG-200 preparation with ¦Á-amylase. However, polysaccharide-free glycogenin proved not to be responsible for the 14C-glucosylation of PG-200. After inactivation of samples by heating, the incubations with UDP-14C-glucose of mixtures of inactive PG-200 with active polysaccharide-free glycogenin and inactive free-glycogenin with active PG-200 resulted in no glucosylation. This indicated the inability of any of both glycogenin species to serve as acceptor for the other. A residual autoglucosylation activity was also observed in the native proteoglycogen fraction isolated from rabbit muscle. The apparent discrepancy between the autoglucosylation of polysaccharide-bound glycogenin and the cessation of polysaccharide-free glycogenin autoglucosylation when the acquired oligosaccharide moiety reached 8-11 glucose units, is discussed.
Supported by FONCYT, CONICET, SECyT-UNC and Agencia C¨®rdoba Ciencia grants
