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Influence of the aromatic moiety in α- and β-arylalanines on their biotransformation with phenylalanine 2,3-aminomutase from Pantoea agglomerans
- Varga, Andrea, Bánóczi, Gergely, Nagy, Botond, Bencze, László Csaba, Toşa, Monica Ioana, Gellért, Ákos, Irimie, Florin Dan, Rétey, János, Poppe, László, Paizs, Csaba
- RSC advances 2016 v.6 no.61 pp. 56412-56420
- Pantoea agglomerans, acrylic acid, ammonia, ammonium carbonate, biocatalysis, biotransformation, byproducts, enantiomers, energy, enzyme substrates, enzymes, isomerization, models, moieties, pH, phenylalanine, stereospecificity
- In this study enantiomer selective isomerization of various racemic α- and β-arylalanines catalysed by phenylalanine 2,3-aminomutase from Pantoea agglomerans (PaPAM) was investigated. Both α- and β-arylalanines were accepted as substrates when the aryl moiety was relatively small, like phenyl, 2-, 3-, 4-fluorophenyl or thiophen-2-yl. While 2-substituted α-phenylalanines bearing bulky electron withdrawing substituents did not react, the corresponding substituted β-aryl analogues were converted rapidly. Conversion of 3- and 4-substituted α-arylalanines happened smoothly, while conversion of the corresponding β-arylalanines was poor or non-existent. In the range of pH 7–9 there was no significant influence on the conversion of racemic α- or β-(thiophen-2-yl)alanines, whereas increasing the concentration of ammonia (ammonium carbonate from 50 to 1000 mM) inhibited the isomerization progressively and decreased the amount of the by-product (i.e. (E)-3-(thiophen-2-yl)acrylic acid was detected). In all cases, the high ee values of the products indicated excellent enantiomer selectivity and stereospecificity of the isomerization except for (S)-2-nitro-α-phenylalanine (ee 92%) from the β-isomer. Substituent effects were rationalized by computational modelling revealing that one of the main factors controlling biocatalytic activity was the energy difference between the covalent regioisomeric enzyme–substrate complexes.