Abstract: Here, a dopa decarboxylase (DDC) from Harmonia axyridis was heterogeneously expressed in Escherichia coli for the efficient biosynthesis of dopamine. For the production of recombinant DDC, the cultivation conditions including IPTG concentration, temperature and induction time were optimized and obtained an optimal specific enzyme activity of 51.72 U·mg^-1 crude extracts. After the purification of DDC with a recovery yield of 68.79%, its activity was further characterized. The V_max, K_m, K_cat, and K_cat/K_m of DDC for dihydroxyphenylalanine (dopa) were 0.02 mmol·ml^-1·s^-1, 2.328 mmol·ml^-1, 10435.90 s^-1 and 4482.77 ml·mmol^-1·s^-1, respectively. The highest DDC activity was observed at the condition of pH 7.5 and 45 ℃. With the purified DDC, the feasibility to produce dopamine from L-dopa was evaluated. The optimal yield was determined at the following bioconversion conditions: pH of 7.0, the reaction temperature of 40 ℃, 0.4 mmol·L^-1 of PLP and 4 g·L^-1 of L-dopa. Subsequently, a fed-batch process for the production of dopamine was developed and the effect of oxygen was evaluated. The titer, yield and productivity of dopamine reached up to 21.99 g·L^-1, 80.88% and 14.66 g·L^-1·h^-1 at 90 min under anaerobic condition.

Key words: Dopa decarboxylase, Dopamine, Enzyme catalysis, Fed-batch bioconversion

摘要： Here, a dopa decarboxylase (DDC) from Harmonia axyridis was heterogeneously expressed in Escherichia coli for the efficient biosynthesis of dopamine. For the production of recombinant DDC, the cultivation conditions including IPTG concentration, temperature and induction time were optimized and obtained an optimal specific enzyme activity of 51.72 U·mg^-1 crude extracts. After the purification of DDC with a recovery yield of 68.79%, its activity was further characterized. The V_max, K_m, K_cat, and K_cat/K_m of DDC for dihydroxyphenylalanine (dopa) were 0.02 mmol·ml^-1·s^-1, 2.328 mmol·ml^-1, 10435.90 s^-1 and 4482.77 ml·mmol^-1·s^-1, respectively. The highest DDC activity was observed at the condition of pH 7.5 and 45 ℃. With the purified DDC, the feasibility to produce dopamine from L-dopa was evaluated. The optimal yield was determined at the following bioconversion conditions: pH of 7.0, the reaction temperature of 40 ℃, 0.4 mmol·L^-1 of PLP and 4 g·L^-1 of L-dopa. Subsequently, a fed-batch process for the production of dopamine was developed and the effect of oxygen was evaluated. The titer, yield and productivity of dopamine reached up to 21.99 g·L^-1, 80.88% and 14.66 g·L^-1·h^-1 at 90 min under anaerobic condition.

关键词: Dopa decarboxylase, Dopamine, Enzyme catalysis, Fed-batch bioconversion