Abstract
L-Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) purified from suspension-cultured cells of French bean (Phaseolus vulgaris) has been further characterized. A number of techniques, including use of an antiserum and affinity probes, have established that all the antigenic polypeptides represent polymorphic Mr forms of the enzyme. These peptides include an apparently higher-Mr (83,000) form which shows different kinetics of induction from the Mr-77000 forms that have been extensively characterized previously. The larger subunit appeared to be PAL by the following criteria: (a) binding to specific affinity and antibody matrices; (b) peptide mapping; (c) active-site labelling; and (d) amino acid composition. The increased Mr of the larger subunit was not completely attributable to glycosylation, although some sugar residues were detected in this Mr-83000 form but not in the other Mr forms. Mr-83000 subunits were also immunoprecipitated from translations in vitro of mRNA from cells that had been stressed for a long period. They were also detected in leaf tissues that were not yet undergoing an extensive wound response. This form of the enzyme may be constitutive and involved in the low-level accumulation of phenolics in most cell types. By contrast, the Mr-77000 forms of PAL were rapidly induced during elicitor action, wounding or cytokinin-induced xylogenesis as a key regulatory enzyme involved in the synthesis of phenolics under stress conditions or during differentiation.