Isolation and characterization of aldose reductase and aldehyde reductase II from bovine lens

Aldose reductase (EC 1.1.1.21) and aldehyde reductase II (L-hexonate dehydrogenase, EC 1.1.1.2) from bovine lens were purified by a combination of DEAE-cellulose, polybuffer exchanger 94, NADP-affinity, and Sephadex G-100 gel filtration chromatographies. Both enzymes are monomers of Mr in the range of 32,000. Aldose reductase has a pI of 5.64 and the pH optimum at 6.2, whereas aldehyde reductase II demonstrate a pI of 6.45 and pH optimum at 7.0. While both the enzymes have wide overlapping substrate specificity and inhibition properties, aldose reductase specifically utilizes aldo-sugars as substrates and is more susceptible to inhibition by Sorbinil and tetramethylene glutaric acid as compared to aldehyde reductase II. Aldehyde reductase II is more susceptible to inhibition by phenobarbital as compared to aldose reductase. The two enzymes are immunologically distinct.