Inactivation and thermal stabilization of glycogenin by linked glycogen

Glycogen-free but not glycogen-bound glycogenin transglucosylates dodecyl-b eta -maltoside. Furthermore, its sugar nucleotide-binding site can be photo affinity labeled using [beta-P-32]5-azido-UDP-glucose. Disruption with DMSO of the hydrogen bonds that stabilize the a-helical structure of glycogen r estored the photoaffinity labeling of the glycogen-bound enzyme but not its transglucosylation activity. The larger size polysaccharide that linked to glycogenin allowed transglucosylation corresponding to that of PG-200, a p roteo-glycogen species Of M-r 200 kDa. PG-200 showed lower activity and inc reased activation energy than glycogen-free glycogenin. Heat denaturation o f glycogen-free and glycogen-bound glycogenin occurred at 51 and 64 degrees C, respectively. Active glycogenin was recovered after the glycogen-bound f orm was heated at 60-70 degreesC and immediately cooled. Treatment at 60 de greesC of the glycogen-free enzyme resulted in inactivation. This is the fi rst report describing the inactivation and thermal stabilization of an enzy me by linked polysaccharide. (C) 2001 Academic Press.