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

To produce dopamine from catechol, pyruvate, and ammonia, an enzymatic proc ess consisting of a two-step reaction, catechol --> L-DOPA --> dopamine, wa s developed. For the first reaction step to synthesize L-DOPA, tyrosine phe nol-lyase of Symbiobacterium sp. SC-1 was used successfully as a biocatalys t, resulting in the high conversion yield of 92%. Two aromatic amino acid d ecarboxylases, rat liver L-DOPA decarboxylase and Streptoccus faecalis tyro sine decarboxylase (TDC), were tested for the subsequent step to produce do pamine. In investigating the effect of L-DOPA concentration, a serious subs trate inhibition of L-DOPA decarboxylase activity was observed at concentra tions over 1 mM, while no inhibition was detected for TDC up to 40 mM L-DOP A. Therefore, the TDC of S. faecalis was selected as the biocatalyst for th e second reaction step. Enzymatic conversion of L-DOPA to dopamine was carr ied out in a reactor controlling the reaction pH with an HCl solution conta ining pyridoxal 5'-phosphate, to compensate for the loss of pyridoxal 5'-ph osphate by an enzyme-catalyzed side reaction, i.e, decarboxylation-dependen t transamination. When the enzyme reactor was operated at 37 degrees 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 teste d for direct synthesis of dopamine, but the productivity was much lower tha n the separated two-step reactions. (C) 1999 Elsevier Science Inc. All righ ts reserved.