The substrate binding site of aldehyde reductase from pig liver. Stereochemical investigations using NADP--2-oxodiacid adducts as probe.

Aldehyde reductase I from pig liver is strongly inhibited by cyclized NADP--2-oxodiacid adducts. This result, in conjunction with those showing a strong inhibitory effect of certain diacid derivatives, such as (+/-)-dimethylsuccinic acid, towards aldehyde reductase I, suggests the presence of two anion sites in or near the substrate binding site. As previously shown to our group [Eur. J. Biochem. 116, 505--512 (1981)], at least one of the two anion sites is an arginine residue. The fact that (2R,3R)-dimethylsuccinic acid is bound more tightly to aldehyde reductase I than the meso and (2S,3S)-dimethylsuccinic acids is indicative of a particular spatial orientation of the two anion sites relative to those of the coenzyme and substrate binding sites of the reductase. This result also supports the idea that one of the two diastereomers of the cyclized adducts, corresponding to the A-side addition product, should exert a stronger inhibitory effect on aldehyde reductase than the other. On the basis of the NMR study made recently by L. J. Arnold et al. [Biochemistry, 18, 2787--2793 (1979)], who determined the conformation and configuration of cyclized pyridine nucleotide adducts, a tentative design of the hydrophobic pocket of the substrate binding site of aldehyde reductase I, containing the two anion sites, is presented.