PURIFICATION OF RABBIT SKELETAL-MUSCLE PROTEOGLYCOGEN - STUDIES ON THE GLUCOSYLTRANSFERASE ACTIVITY OF POLYSACCHARIDE-FREE AND POLYSACCHARIDE-BOUND GLYCOGENIN

Preteoglycogen is the end product in the process of glycogen biogenesi s, We have purified rabbit muscle proteoglycogen and studied the gluco syltransferase reactions catalyzed by its protein moiety, glycogenin, free or bound to the polysaccharide. The purification strategy involve d dissolution of proteoglycogen and cosedimenting membrane vesicles in a Triton X-114/Triton X-45 mixture followed by partition in the aqueo us phase, potassium iodide precipitation of accompanying proteins, and washing by high-speed centrifugation. Glycogenin or a proteoglycogen species of an average molecular mass of 200 kDa was isolated by ion-ex change chromatography after the purified proteoglycogen had been subje cted to long or short amylolytic digestion, respectively, Besides auto glucosylation from UDP-glucose, glycogenin was capable of autogalactos ylation from UDP-galactose. The autoglucosylation reaction was not inh ibited by the simultaneous glucosylation of the exogenous accepters N- (maltosyl-alpha-1-4-(1-deoxiglucitol))peptide or n-dodecyl-beta-D-mait oside. The polysaccharide-bound glycogenin species of 200 kDa showed t o be active for the glucosylation of exogenous acceptor and represente d the isolated proteoglycogen of higher size having glucosyl transfera se activity, This is the first description of the isolation of native proteoglycogen and a proteoglycogen species having glucosyltransferase activity.