Nucleotidases in plants: III. Effect of metabolites on the enzyme hydrolyzing flavine adenine dinucleotide (FAD) from Phaseolus radiatus

Abstract

The highly purified enzyme from mung bean seedlings hydrolyzing FAD at pH 9.4 and temperature 49°, functioned with an initial fast rate followed by a second slower rate. The activity was linear with enzyme concentration over a small range of concentration and was dependent on the time of incubation. Inhibition of enzyme activity with increasing concentrations of AMP was sigmoid; concentrations less than 1 × 10^-6 M were without effect, concentrations between 1 × 10^-6 and 8 × 10^-5 M inhibited by 20% and concentrations beyond 8 × 10^-5 M caused progressive inhibition. Concentrations beyond 1 × 10^-3 M inhibited the activity completely. Preincubation of the enzyme with PCMB or NEM, or aging, or reversible denaturation with urea abolished the inhibitory effect of AMP at concentrations lower than 8 × 10^-6 M. The aged enzyme could be reactivated by ADP.