PARTIAL-PURIFICATION OF A CIS-TRANS-ISOMERASE OF ZEATIN FROM IMMATURESEED OF PHASEOLUS-VULGARIS L

Investigation of the conversion of exogenous cis-zeatin to trans-zeati n in immature seeds of Phaseolus vulgaris L. led to the isolation of a cis-trans-isomerase from the endosperm. The enzyme was purified more than 2000-fold by chromatography on a series of fast protein liquid ch romatography (anion exchange, gel filtration, and hydrophobic interact ion) and concanavalin A columns. The enzymic reaction favors conversio n from the cis to the trans form and requires flavin, light, and dithi othreitol. cis-Zeatin riboside is also a substrate for the enzyme. Ret ention on the concanavalin A column indicated that the enzyme is a gly coprotein. The enzyme was stable for at least 8 weeks when stored at - 80-degrees-C. The occurrence of cis-trans-isomerization suggests that cis-zeatin and cis-zeatin riboside formed by tRNA degradation could be precursors of biologically active cytokinins.