Abstract
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.