NADPD ISOTOPE EFFECT ON ACTIVITY OF EMODIN DEOXYGENASE

Thermoanaerobium brokii alcohol dehydrogenase catalysed the transfer of the pro 4H(s) hydrogen of NADPH. The effect of 4-deuteration of NADPH on the initial rate of conversion of emodin to chrysophanol catalysed by emodin deoxygenase was determined. The deuterium isotope effects on V/K(m) and V(max) with [4R-H-2] NADPH were 1.20 +/- 0.36 and 1.10 +/- 0.11, respectively, The deuterium isotope effects on V/K(m) and V(max) with [4S-H-2]NADPH were 4.08 +/- 1.55 and 6.90 +/- 0.74, respectively. Emodin deoxygenase, therefore, transfers the 4S hydrogen of NADPD in the rate-determining step.