Conversion of gibberellin A20 to gibberellins A 1 and A 5 in a cell-free system from Phaseolus vulgaris.

The soluble fraction of a cell-free system from immature seeds of Phaseolus vulgaris L. converts gibberellin A20 (GA20) to GA1 and GA5. It does however not metabolize GA1 and GA29 to GA5, showing that in this system GA20 is converted directly to GA5. The steps from GA20 to GA1 (3-hydroxylation) and from GA20 to GA5 (Δ(2) double-bond formation) require oxygen, Fe(2+) and α-ketoglutarate, and are stimulated by ascorbate. The enzymes catalyzing these conversions bate. The enzymes catalyzing these conversions have properties similar to those of GA oxidases found in Cucurbita maxima and Pisum sativum.