NADPH-dependent reductases of the dog lens

The presence of several NADPH-dependent reductases has been observed in the dog lens. Applying the purification procedures of gel filtration, affinity chromatography and chromatofocusing to dog lens homogenates resulted in the purification of aldose reductase. This enzyme appeared similar to dog kidney aldose reductase in molecular weight, isoelectric point, kinetic properties, and susceptibility to inhibition by aldose reductase inhibitors. Evidence for the presence of trace amounts of aldehyde reductase in the dog lens was also observed, although this enzyme is not present in sufficient quantities for isolation and characterization. The presence of a labile third enzyme that is immunologically distinct from either aldose reductase or aldehyde reductase was also detected. This enzyme utilizes only glyceraldehyde as substrate and is not inhibited by aldose reductase inhibitors.