INFLUENCE OF CHAIN SIZE AND MOLECULAR-WEIGHT ON KINETIC CONSTANTS FOR SPAN GLUCOSE TO POLYSACCHARIDE FOR RABBIT MUSCLE GLYCOGEN SYNTHASE

The kinetic constants for the series of glucosyl acceptors for homogeneous rabbit muscle glycogen synthase I form free of glycogen were examined. The acceptors included glucose, maltose, G3 [maltotriose], G4 [maltotetraose, potato starch], G6 [maltohexaose], 2 hydrolyzed amyloses, amylodextrin and 7 polysaccharides including amylopectin and glycogen. S0.5 [1/2 maximal substrate concentration] and relative Vmax were estimated in each case. From these data a 2 site model for the enzyme is proposed, composed of a polysaccharide binding site and a separate catalytic site, the latter composed of several subsites.