, Volume 26, Issue 4, pp 305-312

Biotransformation of phenylpyruvic acid to l-phenylalanine using a strain of Pseudomonas fluorescens ATCC 11250 with high transaminase activity

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Abstract

The rate of l-phenylalanine production from phenylpyruvic acid by whole cells of Pseudomonas fluorescens strain ATCC 11250 was greater than 3 g·l-1 h-1. Synthesis of transaminase was constitutive but activity was greatest in medium containing d- or l- phenylalanine as sole nitrogen source. Maximum conversion was observed at 34–40° C and at alkaline pH, with over six times initial rate of conversion at pH 12 than at pH 5. The optimum catalyst (cell) concentration was between 10–20 mg ml-1 dry weight. The initial rate of conversion was directly proportional to phenylpyruvate concentration, up to 4%, but the conversion yield steadily decreased between 2% and 4% substrate concentration. The rate of conversion, as expected, increased as the concentration of glutamate increased. Whole cells were still capable of over 63% conversion after 40 days providing reactions were supplemented with pyridoxal phosphate. Immobilisation of cells in calcium alginate and operation of a packed bed bioreactor enabled the continuous production of l-phenylalanine in concentrations greater than 15 g·l-1 after 60 days operation.