A comparison of the activator sites of liver and muscle glycogen phosphorylase b.
Characteristics of the activator sites of liver and muscle phosphorylase b were probed by using AMP and AMP analogs in kinetic studies, by quantitative affinity chromatography, and by reaction with an affinity-labeling reagent. Activation of liver phosphorylase b by N6-(6-aminohexyl)AMP in comparison with AMP and other analogs is explained by preferential binding to the activator site. The KM value for glucose-1-P of liver phosphorylase b activated with N6-(6-aminohexyl)AMP is considerably higher than that of muscle phosphorylase b. Affinity chromatography utilizing AMP-Sepharose suggests that the activator site is less well formed in liver phosphorylase than in muscle phosphorylase. Reaction with 8-[m-(m-fluorosulfonylbenzamido)benzylthio]adenine activates liver phosphorylase b and is consistent with the reaction at the activator site. The results suggest that part of the reason that liver phosphorylase b is not activated by AMP and AMP analogs is due to a poor coupling between the activator and active sites. Lack of good activation by AMP also can be explained by binding at the inhibitor site.
D000249:Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002110:Caffeine / Q000494:pharmacology; D004789:Enzyme Activation; D005947:Glucose / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology*; D009928:Organ Specificity; D010763:Phosphorylase b / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits
D002110:Caffeine; D000249:Adenosine Monophosphate; D010763:Phosphorylase b; D006005:Phosphorylases; D005947:Glucose