Human NRDRB1, an alternatively spliced isoform of NADP(H)-dependent retinol dehydrogenase/reductase enhanced enzymatic activity of benzil.

Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology

PubMedID: 23128527

Yan Y, Song X, Liu G, Su Z, Du Y, Sui X, Chang X, Huang D. Human NRDRB1, an alternatively spliced isoform of NADP(H)-dependent retinol dehydrogenase/reductase enhanced enzymatic activity of benzil. Cell Physiol Biochem. 2012;30(6):1371-82.
AIMS
Human NRDRB1, a 226 amino acid alternatively spliced isoform of the NADP(H)- dependent retinol dehydrogenase/reductase (NRDR), lacks the complete coding region of exon 3, but preserves all the important functional motifs for NRDR catalytic activity. Nevertheless, its tissue distribution and physiological function remain to be elucidated.

METHODS
Expression of NRDRB1 and NRDR in cells and tissues was analyzed by semi-quantitative polymerase chain reaction (PCR) and western blot. NRDRB1 was expressed as a His(6) fusion protein and subjected to kinetics assays.

RESULTS
Recombinant NRDRB1 had 1.2 to 8.6 fold higher k(cat)/K(m) values than recombinant NRDR, depending on the substrate. NRDRB1 catalyzed the NADPH-dependent reduction of a-dicarbonyl compounds, such as isatin, 9,10-phenanthrenequinone, and especially benzil. The significantly high catalytic activity and the relatively high expression in human liver of NRDRB1 conferred cellular resistance to benzil-induced cell toxicity and over-expression of NRDRB1 in low expressing Ec109 cells significantly enhanced cell tolerance toward benzil.

CONCLUSIONS
Based on its substrate specificity, catalytic activity and relatively high expression in human liver tissue, our results suggest that NRDRB1, an alternatively spliced isoform of NRDR in vivo functions better than NRDR as a dicarbonyl reductase for xenobiotics containing reactive carbonyls. Our study is the first reporting this phenomenon of the enzymes involved in biochemical reactions.