Structural changes induced in glycogen phosphorylase b by the binding of glucose and caffeine.
The allosteric inhibitors glucose and caffeine cause significant structural alterations in glycogen phosphorylase b (1,4-alpha-D-glucan:orthophosphate alpha-D-glucosyltransferase, EC 2.4.1.1). Both cause a masking of two sulfhydryl groups and a reduction of binding affinity for AMP. Caffeine produces an alteration in the microenvironment of the binding site for 1-anilin-naphthalene-8-sulfonate, resulting in a decrease of quantum yield of fluorescence and a change in spectral distribution. The binding of glucose is exothermic with an enthalpy of binding of -6.0 kcal/mol. Glucose causes a change in the molecular ellipticity in the pyridoxal-5'-phosphate region. The implications of these results are discussed.
D000249:Adenosine Monophosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002151:Calorimetry; D002942:Circular Dichroism; D005947:Glucose / Q000494:pharmacology*; D009132:Muscles / Q000201:enzymology; D010763:Phosphorylase b / Q000037:antagonists & inhibitors*; D006005:Phosphorylases / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000378:metabolism
D000817:Anilino Naphthalenesulfonates; D013438:Sulfhydryl Compounds; D002110:Caffeine; D000249:Adenosine Monophosphate; D010763:Phosphorylase b; D006005:Phosphorylases; D005947:Glucose