Properties of an Aldose Reductase from Pig Lens

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Abstract
Two monomeric NADPH enzymes from pig lens, an aldehyde reductase and an aldose reductase, were characterized. The aldose reductase is obtained in a pure form. The aldehyde reductase, usually called hexonate dehydrogenase, is the same protein as that recently isolated from pig liver. The aldose reductase has number of properties in common with the aldehyde reductase, e.g., its physico-chemical properties, its tendency to be inhibited by quercitine derivatives and its substrate specificity. These 2 enzymes differ in their immunological properties. Only aldose reductase has a reactive Cys residue, localized in or near the substrate binding site. In contrast to that shown for aldehyde reductase no anion-recognition sites are in the substrate binding site of aldose reductase. The fact that sugars are also substrates for aldose reductase supports the idea that this enzyme is implicated in the formation of sugar cataract as suggested by Kinoshita et al. Pig lens aldose reductase does not show homotropic cooperative effects with respect to either substrate or coenzyme.