Efficient production of L-phenylalanine catalyzed by a coupled enzymatic system of transaminase and aspartase

摘要

A process for efficient production of L-phenylalanine catalyzed by a coupled enzymatic system of transaminase and aspartase with two organisms was developed.One strain,Escherichia coli EP8-10 produces significant transaminase and less aspartase under incubation in the glucose-beef extract medium.In the presence of 50 mg/ml cells of EP8-10,0.24 mol/l phenylpyruvic acid(PPA)was converted to L-phenylalanine(L-Phe)in 8 h with L-aspartic acid as an amine donor,the conversion rate was 97%.Another strain,E.coli EA-1,a mutant strain of ATCC11303,produces significant aspartase and less transaminase.L-Aspartate(L-Asp),the amine donor,could be produced by EA-1 from fumarate(Fu)and ammonia.In presence of the mixture of EP8-10 and EA-1 cell,L-phenylalanine was efficiently produced from PPA and ammonium fumarate.An optimum reaction condition of the coupled enzymatic system is a follows:the concentration ratio of two cells as 0.4:1(EA-1 to EP8-10),concentration ratio of two substrates(PPA to Fu)as 1:1.2(mol).When concentration of PPA was 0.24,0.233 mol/l(38 g/l),L-phenylalanine acid was accumulated by the conversion rate up to 97%.L-Phenylalanine production is more economical by the coupled enzymatic system,since one of the substrates L-aspartate was replaced by the relative cheap fumaric acid.