A Monoclonal Antibody Specific to Zeatin O-Glycosyltransferases of Phaseolus

Zeatin O-xylosyltransferase and zeatin O-glucosyltransferase occur in immature embryos of Phaseolus vulgaris and P. lunatus, respectively. Purified preparations of the xylosyltransferase were used as antigen to elicit the formation of antibodies in mice. Hybridoma clones were produced by fusion of mouse spleen cells with myeloma cell line Fox-NY. A clone secreting monoclonal antibody (MAb), XZT-1, capable of immunoprecipitating both enzymes was obtained. The MAb detected a unique protein band from crude embryo extracts of each species with the correct molecular mass (50 kilodaltons) and relative charge (R(F) = 0.5 and 0.3) of the respective enzymes. Competition experiments with substrates indicated that the glycosyl dinucleotide binding sites of the enzymes are probably not involved in MAb-enzyme recognition. Western blotting of samples from vegetative tissues of P. vulgaris detected a low level of O-glucosyltransferase but not O-xylosyltransferase, in leaves. These findings suggest the occurrence of two genes in P. vulgaris coding for O-glycosylation enzymes with tissue-specific expression. The MAb will be used to screen expression libraries and to obtain pure enzymes for amino acid sequencing and for the production of additional MAbs.