Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

Abstract

Rabbit muscle aldolase catalyzed the exchange with solvent of all 3 methyl hydrogens of hydroxyacetone phosphate. Under saturating conditions, rates of the following processes were measured: deuteration of hydroxyacetone phosphate in 2H2O (by an NMR method), tritiation of hydroxyacetone phosphate in H2O and 2H2O and detritiation of 3H-hydroxyacetone phosphate in H2O and 2H2O. There was no primary kinetic isotope effect and H abstraction was not rate-determining to the exchange. Only 1 (as the closest integer) methyl H exchanged per turnover. These observations were mutually exclusive in terms of the accepted aldolase mechanism in the absence of further restrictions imposed by the enzyme. Possible restrictions were discussed.