title: Enhanced conversion of racemic alpha-arylalanines to (R)-beta-arylalanines by coupled racemase/aminomutase catalysis.
abstract: The Taxus phenylalanine aminomutase (PAM) enzyme converts several (S)-alpha-arylalanines to their corresponding (R)-beta-arylalanines. After incubating various racemic substrates with 100 microg of PAM for 20 h at 31 degrees C, each (S)-alpha-arylalanine was enantioselectively isomerized to its corresponding (R)-beta-product. With racemic starting materials, the ratio of (R)-beta-arylalanine product to the (S)-alpha-substrate ranged between 0.4 and 1.8, and the remaining nonproductive (R)-alpha-arylalanine became enriched. To utilize the (R)-alpha-isomer, the catalysis of a promiscuous alanine racemase from Pseudomonas putida (KT2440) was coupled with that of PAM to increase the production of enantiopure (R)-beta-arylalanines from racemic alpha-arylalanine substrates. The inclusion of a biocatalytic racemization along with the PAM-catalyzed reaction moderately increased the overall reaction yield of enantiopure beta-arylalanines between 4% and 19% (depending on the arylalanine), which corresponded to as much as a 63% increase compared to the turnover with the aminomutase reaction alone. The use of these biocatalysts, in tandem, could potentially find application in the production of chiral beta-arylalanine building blocks, particularly, as refinements to the process are made that increase reaction flux, such as by selectively removing the desired (R)-beta-arylalanine product from the reaction mixture.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Brad M
authors.initials: BM
authors.lastname: Cox
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Bilsborrow
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Walker
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000096:biosynthesis* / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D001665:Binding Sites; D055162:Biocatalysis; D010650:Phenylalanine Ammonia-Lyase / Q000378:metabolism*; D016958:Pseudomonas putida / Q000201:enzymology*; D019998:Racemases and Epimerases / Q000378:metabolism*; D013237:Stereoisomerism; D020946:Taxus / Q000201:enzymology*
chemical_list: D001555:Benzene Derivatives; D010650:Phenylalanine Ammonia-Lyase; D019998:Racemases and Epimerases; D000409:Alanine