... AG,Marburg, Germany).Enzyme assay and protein determinationHAL activity was measured spectrophotometrically at 25 8Cfollowing the formation of trans-urocanate at 277 nm. The assay was performed in 1-cm ... (reviewed in [1]). An analogous mechanismwas proposed for the reaction catalysed by the homologousenzyme phenylalanine ammonia-lyase (PAL, EC 4.3.1.5)which convertsL-phenylalanine into trans-cinnamic ... coordinatingwater O , imidazolyl-N1 of the histidine, Asn195coordinating water O , NH31 of histidine, and S atom of the sulfate anion , carboxylate C of histidine. Afterdocking, the sulfate...