PARTIAL-PURIFICATION OF 2 GIBBERELLIN 2-BETA-HYDROXYLASES FROM COTYLEDONS OF PHASEOLUS-VULGARIS

Two gibberellin (GA) 2-beta-hydroxylases were partially purified from cotyledons of mature seeds of Phaseolus vulgaris. The enzymes were separated by cation exchange chromatography on S-Sepharose and designated enzyme I and enzyme II in order of elution. They differed in their apparent M(r) and in their specificities for C-19-GA substrates. The 3-beta-hydroxy GAs, GA1 and GA4, were more effective substrates for enzyme I than were the non-3-beta-hydroxy GAs, GA9 and GA20. In contrast, GA9 was the preferred substrate for enzyme II. The enzymes had similar pH optima (pH 6-7) and required 2-oxoglutarate, ascorbate and Fe2+ for activity. The apparent K(m) values for 2-oxoglutarate for 2-beta-hydroxylation of [1,2-H-3(2)]GA1 by enzyme I and of [2,3-H-(2)]GA9 by enzyme II were 11.8 and 4.5-mu-M, respectively.