Preparation and properties of the glycogen-debranching enzyme from rabbit liver

Abstract

The glycogen-debranching enzyme, oligo-α-1,4-glucan: α-1,4-glucan-4-glycosyl-transferase-amylo-1,6-glucosidase has been purified about 500-fold from rabbit liver. The enzyme preparation has been shown to have both transferase and glucosidase activities. In view of the fact that the protein moves as one band in discgel electrophoresis and possesses the two activities in constant ratio throughout its purification, it is concluded that one protein in fact possesses both activities. The molecular weight of the enzyme has been found to be about 179 000 by sucrose-density gradient centrifugation. The enzyme is strongly inhibited when assayed in Tris buffer and somewhat less so in imidazole buffer as compared with citrate or phosphate buffers in which the optimum for activity is at about pH 6 when a limit dextrin of glycogen, prepared by prior phosphorylase action, is the substrate. Enzyme activity is also reversibly inhibited by urea at concentrations below 2 M. Guanidine at 0.15 M produces 50% inhibition of glucose formation from a phosphorylase limit dextrin.