Preparation and characterization, using high-performance liquid chromatography, of an enzyme forming glucosides of cytokinins

Cytokinins can occur naturally as glycosides with β-d-glucose as the sugar substituent. From radish (Raphanus sativus) cotyledons, and enzyme has been partly purified which synthesizes the 7-glucopyranoside of zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine], a compound known to occur in this species. High-performance reverse-phase liquid chromatography was uniquely useful as the analytical procedure for quantitative study of the minute amounts of enzyme available. The enzyme uses UDPglucose as the source of the sugar residue. A large number of derivatives of purine are glucosylated, but adenine derivatives with an alkyl side chain at least three carbon atoms in length at position N⁶ are preferentially glucosylated. This corresponds to the structural features required for high cytokinin activity. The 7-glucoside of zeatin is known to be very weakly active in cytokinin bioassays. Hence, this enzyme, and other catalyzing the same reaction, have a role in the regulation of cytokinin activity.