title: Effect of osmolytes on the interaction of flavin adenine dinucleotide with muscle glycogen phosphorylase b.
abstract: The effect of three osmolytes, trimethylamine N-oxide (TMAO), betaine and proline, on the interaction of muscle glycogen phosphorylase b with allosteric inhibitor FAD has been examined. In the absence of osmolyte, the interaction is described by a single intrinsic dissociation constant (17.8 microM) for two equivalent and independent binding sites on the dimeric enzyme. However, the addition of osmolytes gives rise to sigmoidal dependencies of fractional enzyme-site saturation upon free inhibitor concentration. The source of this cooperativity has been shown by difference sedimentation velocity to be an osmolyte-mediated isomerization of phosphorylase b to a smaller dimeric state with decreased affinity for FAD. These results thus have substantiated a previous inference that the tendency for osmolyte-enhanced self-association of dimeric glycogen phosphorylase b in the presence of AMP was being countered by the corresponding effect of molecular crowding on an isomerization of dimer to a smaller, nonassociating state.
authors.affiliation: AN Bakh Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russian Federation.
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Chebotareva
authors.forename: Boris I
authors.initials: BI
authors.lastname: Kurganov
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Harding
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Winzor
mesh_terms: D000818:Animals; D001622:Betaine / Q000494:pharmacology*; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism*; D024982:Glycogen Phosphorylase, Muscle Form / Q000378:metabolism*; D008744:Methylamines / Q000494:pharmacology*; D009994:Osmolar Concentration; D010763:Phosphorylase b / Q000378:metabolism*; D011392:Proline / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D011817:Rabbits
chemical_list: D008744:Methylamines; D005182:Flavin-Adenine Dinucleotide; D001622:Betaine; D011392:Proline; D024982:Glycogen Phosphorylase, Muscle Form; D010763:Phosphorylase b; C005855:trimethyloxamine