The conversion of gibberellin A1 to gibberellin A 8 by a cell-free enzyme system.

An enzyme system which catalyzes hydroxylation of (3)[H]gibberellin A1 ([(3)H]GA1) to [(3)H]GA8 was obtained from homogenates of germinating bean (Phaseolus vulgaris L.) seed. The system remained in the supernatant after centrifugation at 95000×g for 2 h. Hydroxylation occurred at one of the specifically (3)H-labeled positions (C-2) and, concomitantly, produced [(3)H]water whic was used to measure formation of [(3)H]GA8. NADPH and/or ascorbate are cofactors utilized by this enzyme. EDTA effectively inhibited the system, suggesting a cation requirement.