Aldose Reductase from Porcine Liver Metabolizing 3-Deoxyglucosone, a Maillard Reaction Intermediate.

An enzyme which catalyzes the NADPH-dependent reduction of 3-deoxyglucosone (3DG) was isolated and purified from porcine liver by ammonium sulfate fractionation, and DEAE-cellulose, hydroxyapatite, Sephadex G-100, Blue Sepharose CL-6B, and Sephadex G-100 column chromatographies. The pH for optimum enzyme activity was 6.5. 3DG was a good substrate, and glucose and fructose could also be reduced at a significant rate. The Km values for 3DG, methylglyoxal and glyceraldehyde were 2.5, 1.9, and 4.9 mM, respectively. The molecular mass of the enzyme was estimated to be 67, 000, and the enzyme is proposed to be a dimer composed of identical subunits. The activity of the enzyme was completely inhibited by p-chloromercuribenzoate, and the enzyme is estimated to be an aldose reductase.