Spectrophotometric assays were carried out with a Beckman
DU-60 spectrophotometer, supplied with a Kinetics
Soft-Pac module and temperature incubator set at 30°C
(Beckman, Fullerton, CA, USA). Absorption was measured
at 340 nm, and reaction rates were linearly proportional to
the amount of extract added. One unit is defined as the
conversion of 1 mmol of NAD(P)H per min.