title: The catalytic bimodality of mammalian phosphoglycerate mutase.
abstract: Rabbit muscle phosphoglycerate mutase, presumed to manifest an absolute cofactor requirement for activity, has been found to express catalysis (3 +/- 1% of optimum) in the absence of added D-glycerate-2,3-P2. Isotope experiments indicate that this catalysis proceeds through a binary phosphoryl enzyme-glycerate intermediate which dissociates into free enzyme and monophosphoglycerate. 32P-Labeled phosphoglycerate mutase is formed by reaction with either D-32P-glycerate-3-P or D-U32P-glycerate-2,3-P2. In each case, the acid lability and alkali stability of the covalent adduct, phosphoenzyme, is consistent with a phosphohistidyl residue having been formed within the active site. D-[U-14C]Glycerate reacts with phosphoenzyme to generate D-[U-14C]monophosphoglycerate which, in turn, can react further with phosphoenzyme to yield D-[U-14C]glycerate-2,3-P2. The pH profile for the cofactor-independent activity exhibits an optimum at 6.0 as opposed to 7.0 when D-glycerate-2,3-P2 is present in the reaction medium. Bisubstrate kinetics (pH 7.0, 23 degrees C) with D-glycerate-3-P concentration as the variable, yields a family of reciprocal plots which is in accord with a modified ping-pong mechanism when D-glycerate-2,3-P2 concentrations are greater than 10(-1) Km (where Km = 0.33 microM). Progressively diminishing concentrations (much less than Km) of D-glycerate-2,3-P2 produce curvilinear reciprocal plots that approach linearity as a limit in accordance with single substrate kinetics.
mesh_terms: D019794:2,3-Diphosphoglycerate; D000818:Animals; D001731:Bisphosphoglycerate Mutase / Q000378:metabolism*; D004163:Diphosphoglyceric Acids / Q000378:metabolism; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008433:Mathematics; D009132:Muscles / Q000201:enzymology; D010770:Phosphotransferases / Q000378:metabolism*; D011817:Rabbits
chemical_list: D004163:Diphosphoglyceric Acids; D046911:Macromolecular Substances; D019794:2,3-Diphosphoglycerate; D010770:Phosphotransferases; D001731:Bisphosphoglycerate Mutase