Crystalline D-Mannitol:NAD Oxidoreductase from Leuconostoc mesenteroides

Part II. Substrate and Coenzyme Specificity

Abstract

The crystalline D-mannitol dehyrogenase (D-mannitol:NAD oxidoreductase, EC 1.1.1.67) catalyzed the reversible reduction of D-fructose to D-mannitol. D-Sorbitol was oxidized only at the rate of 4%0 of the activity for D-mannitol. The enzyme was inactive for all of four pentitols and their corresponding 2-ketopentoses. The apparent optimal pH for the reduction of D-fructose or the oxidation of D-mannitol was 5.35 or 8.6, respectively. The Michaelis constants were 0.035M for D-fructose and 0.020M for D-mannitol. The enzyme was also found to be specific for NAD. The Michaelis constans were 1×10^-5M for NADH₂ and 2.7×10^-4M for NAD.