Optimization of oligomeric enzyme activity in ionic liquids using Rhodotorula glutinis yeast phenylalanine ammonia lyase

•Phenylalanine ammonia lyase (PAL) enzyme activity of Rhodotorula glutinis has been demonstrated in four commonly used ionic liquids.•Enzyme activity of oligomeric PAL protein in the reaction mixture containing 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) is comparable to that obtained in aqueous buffer medium.•Various conditions were standardized for optimal PAL forward activity in the reaction mixture containing [BMIM][PF6]; about 83% conversion of L-phenylalanine to trans-cinnamic acid was obtained.•PAL reverse activity in ionic liquids was shown for the first time; about 59% conversion of trans-cinnamic acid to L-phenylalanine was obtained in the reaction mixture containing [BMIM][PF6].

Phenylalanine ammonia lyase (E.C.4.3.1.24, PAL) activity of Rhodotorula glutinis yeast has been demonstrated in four commonly used ionic liquids. PAL forward reaction was carried out in 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and 1-butyl-3-methylimidazolium lactate ([BMIM][lactate]). Our experiments have revealed that PAL is catalytically active in ionic liquids and the enzyme activity in ([BMIM][PF6]) is comparable to that obtained in aqueous buffer medium. Different conditions were optimized for maximal PAL forward activity including time of incubation (30.0 min) L-phenylalanine substrate concentration (30.0 mM), nature of buffer (50.0 mM Tris-HCl), pH (9.0), temperature (37 °C), and speed of agitation (100 rev min−1). Under these optimized conditions, about 83% conversion of substrate to product was obtained for the PAL forward reaction that was determined using UV spectroscopy at 290 nm. PAL reverse reaction in ([BMIM][PF6]) was determined spectrophotometrically at 520 nm; and about 59% substrate conversion was obtained. This data provides further knowledge in enzyme biocatalysis in non-aqueous media, and may be of importance when studying the function of other oligomeric/multimeric proteins and enzymes in ionic liquids.