PURIFICATION AND PROPERTIES OF ALDEHYDE REDUCTASES FROM HUMAN-PLACENTA

Aldehyde reductases (alcohol:NADP+-oxidoreductase, EC 1.1.1.2) I and II from human placenta were purified to homogeneity. Aldehyde reductase I, MW about 74,000, is a dimer of 2 nonidentical subunits of MW of about 32,500 and 39,000; aldehyde reductase II is a monomer of about 32,500. Aldehyde reductase I can be dissociated into subunits under high ionic concentrations. The isoelectric pH for aldehyde reductases I and II and 5.76 and 5.20, respectively. Amino acid compositions of the 2 enzymes are significantly different. Placenta aldehyde reductase I can utilize glucose with a lower affinity; aldehyde reductase II is not capable of reducing aldo-sugars. Similarly, aldehyde reductase I does not catalyze the reduction of glucuronate while aldehyde reductase II has a high affinity for glucuronate. Both enzymes exhibit strong affinity towards various other aldehydes such as glyceraldehyde, propionaldehyde and pyridine-3-aldehyde. The pH optima for aldehyde reductases I and II and 6.0 and 7.0, respectively. Aldehyde reductase I can use both NADH and NADPH as cofactors; aldehyde reductase II activity is dependent on NADPH only. Both enzymes are susceptible to inhibition by sulfhydryl group reagents, aldose reductase inhibitors, lithium sulfate and sodium chloride to varying degrees.