Enzyme relaxation in the reaction catalyzed by triosephosphate isomerase: detection and kinetic characterization of two unliganded forms of the enzyme.
Triosephosphate isomerase has been shown to exist in two unliganded forms, one of which binds and isomerizes (R)-glyceraldehyde 3-phosphate and the other of which binds and isomerizes dihydroxyacetone 3-phosphate. The tracer perturbation method of Britton demonstrates the kinetic significance of the interconversion of these two enzyme forms at high substrate concentrations and yields a rate constant of about 10(6) s-1 for the interconversion. Although the molecular nature of the two forms of unliganded enzyme is not defined by these experiments, a shuffling of protons among active site residues, or a protein conformational change, or both, may be involved. This study, coupled with the known rate constants for the substrate-handling steps of triosephosphate isomerase catalysis, completes the kinetic characterization of the catalytic cycle for this enzyme.
Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138.
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Raines
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Knowles
D000818:Animals; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D002645:Chickens; D007700:Kinetics; D008024:Ligands; D008433:Mathematics; D008962:Models, Theoretical; D009132:Muscles / Q000201:enzymology; D011487:Protein Conformation; D014305:Triose-Phosphate Isomerase / Q000378:metabolism*
D008024:Ligands; D002238:Carbohydrate Epimerases; D014305:Triose-Phosphate Isomerase