pH-dependence of the triose phosphate isomerase reaction.

The pH-dependences of the kinetic parameters k(cat.) and K(m) for the triose phosphate isomerase reaction were determined in each direction. Apparent pK(a) values of 6.0 and 9.0 are observed in the dependences of k(cat.)/K(m). The pH-dependences of k(cat.) are sigmoid, with apparent pK(a) values of about 6.0. The results are interpreted in terms of a single base on the enzyme providing an efficient proton-shuttling mechanism for the isomerization.