Daunorubicin reduction mediated by aldehyde and ketone reductases

1. The cancer chemotherapeutic antibiotic, daunorubicin, is metabolized in rabbit liver by two distinct cytoplasmic reductases, with pH optima at 6.0 and 8.5. 2. A comparison of inhibition and activation of these two enzymes provides evidence of biochemical and kinetic differences, and suggests that the enzymes belong to different classes of carbonyl reductases; the pH 8.5 optimum reductase activity is classified as an aldehyde reductase, whereas the pH 6.0 optimum reductase is a ketone reductase.