Repeated batch production of L‐phenylalanine from phenylpyruvate and NH₄Cl by immobilized cells of Nocardia opaca under hydrogen high pressure

Among various microbial cells examined under screening conditions, Nocardia opaca showed the highest activity for production of phenylalanine from phenylpyruvate. Here NH₄Cl as well as amino acids were used as an amino donor for phenylalanine production. The phenylalanine production rate increased with increasing hydrogen pressure. The specific activity of phenylalanine dehydrogenase was increased by culturing N. opaca cells in nutrient broth containing 0.3% phenylalanine. As a result, the phenylalanine production rate increased from 0.69 to 4.4 μmol/min g dry cells. Immobilized cells were activated in nutrient broth containing ZnCl₂ before phenylalanine production. Phenylalanine dehydrogenase activity and cell number in the gel increased with increasing incubation time, and the maximum phenylalanine dehydrogenase activity was obtained at 36 h incubation. Then, phenylalanine was produced from phenylpyruvate, NH₄Cl, and 100 atm H₂ with the activated immobilized cells. The rate of phenylalanine production was 0.24 μmol/min cm³ gel. The conversion of phenylpyruvate to phenylalanine was 82%. Immobilized cells retained 76% of the initial phenylalanine production rate after 10 h reactions were repeated 11 times with two intervening reactivations.