Development of an enzymatic system for the production of dopamine from catechol, pyruvate, and ammonia

Abstract

To produce dopamine from catechol, pyruvate, and ammonia, an enzymatic process consisting of a two-step reaction, catechol → l-DOPA → dopamine, was developed. For the first reaction step to synthesize l-DOPA, tyrosine phenol-lyase of Symbiobacterium sp. SC-1 was used successfully as a biocatalyst, resulting in the high conversion yield of 92%. Two aromatic amino acid decarboxylases, rat liver l-DOPA decarboxylase and Streptoccus faecalis tyrosine decarboxylase (TDC), were tested for the subsequent step to produce dopamine. In investigating the effect of l-DOPA concentration, a serious substrate inhibition of l-DOPA decarboxylase activity was observed at concentrations over 1 mM, while no inhibition was detected for TDC up to 40 mM l-DOPA. Therefore, the TDC of S. faecalis was selected as the biocatalyst for the second reaction step. Enzymatic conversion of l-DOPA to dopamine was carried out in a reactor controlling the reaction pH with an HCl solution containing pyridoxal 5′-phosphate, to compensate for the loss of pyridoxal 5′-phosphate by an enzyme-catalyzed side reaction, i.e. decarboxylation-dependent transamination. When the enzyme reactor was operated at 37°C for 12 h, 100 mM of l-DOPA was converted to dopamine with the conversion yield of 100%. Simultaneous reactions of tyrosine phenol-lyase and TDC were tested for direct synthesis of dopamine, but the productivity was much lower than the separated two-step reactions.