Specificity and kinetics of triose phosphate isomerase from chicken muscle

Abstract

The isolation of crystalline triose phosphate isomerase from chicken breast muscle is described. The values of kcat. and Km for the reaction in each direction were determined from experiments over wide substrate-concentration ranges, and the reactions were shown to obey simple Michaelis–Menten kinetics. With d-glyceraldehyde 3-phosphate as substrate, kcat. is 2.56×105min-1and Km is 0.47mm; with dihydroxyacetone phosphate as substrate, kcat. is 2.59×104min-1and Km is 0.97mm. The enzyme-catalysed exchange of the methyl hydrogen atoms of the ‘virtual substrate’ monohydroxyacetone phosphate with solvent2H2O or3H2O was shown. This exchange is about 104-fold slower than the corresponding exchange of the C-3 hydrogen of dihydroxyacetone phosphate. The other deoxy substrate, 3-hydroxypropionaldehyde phosphate, was synthesized, but is too unstable in aqueous solution for analogous proton-exchange reactions to be studied.