Near-full-length cDNAs for the four phenylalanine ammonia-lyase (PAL) isoenzymes in parsley (Petruselinum crispum Nym.) were cloned and the complete amino acid sequences deduced. Fusion proteins with glutathione S-transferase were expressed in Escherichia coli, purified and cleaved. All of the resulting phenylalanine ammonia-lyase proteins, as well as the fusion proteins, were catalytically active. The turnover number of one selected isoenzyme, PAL-1, was estimated to be around 22 s-' for each active site. In contrast to a certain degree of differential expression in various parts of parsley plants, the four phenylalanine ammonia-lyase isoenzymes exhibited very similar apparent K,,, values for L-phenylalanine (15-24.5 pM) as well as identical temperature (58°C) and pH (8.5) optima. All of them were competitively inhibited by (E)-cinnamate with similar efficiency (K, values: 9

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