Identification and Characterization of an Efficient Phenylalanine Ammonia-Lyase from Photorhabdus luminescens

A putative aromatic amino acid ammonia-lyase gene (named Pl-pal ) was discovered in Photorhabdus luminescens DSM 3368. BLAST and phylogenetic analyses predicted that this enzyme is a histidine ammonia-lyase, whereas sequence alignment suggested that it is more likely a phenylalanine ammonia-lyase (PAL). This gene was amplified from P. luminescens and expressed in Escherichia coli BL21(DE3). The function of Pl -PAL (58 kDa) was characterized by in vitro enzymatic reactions with l -phenylalanine ( l -Phe), l -tyrosine ( l -Tyr), l -histidine ( l -His), and l -tryptophan ( l -Trp). Pl -PAL can convert l -Phe and l -Tyr to trans -cinnamic acid and p -coumaric acid, respectively, but had no function on l -His and l -Trp. The optimum temperature and pH were determined to be 40 °C and 11.0, respectively. Under the optimal conditions, Pl -PAL had a k cat / K m value of 0.52 s −1 mM −1 with l -Phe as the substrate, while only 0.013 s −1 mM −1 for l -Tyr. Therefore, the primary function of Pl -PAL was determined to be PAL. The Pl-pal -harboring E. coli strain was used as a whole-cell biocatalyst to produce trans -cinnamic acid from l -Phe. The overall molar conversion rate and productivity were 65.98% and 228.10 mg L −1 h −1 , respectively, after the cells were repeatedly utilized 7 times. This work thus provides a promising strain for industrial production of trans -cinnamic acid.