Characterization of a Novel Shewanella algae Arginine Decarboxylase Expressed in Escherichia coli

Arginine decarboxylase (ADC) catalyzes the decarboxylation of arginine to form agmatine, an important physiological and pharmacological amine, and attracts attention to the enzymatic production of agmatine. In this study, we for the first time overexpressed and characterized the marine Shewanella algae ADC (SaADC) in Escherichia coli. The recombinant SaADC showed the maximum activity at pH 7.5 and 40 °C. The SaADC displayed previously unreported substrate inhibition when the substrate concentration was higher than 50 mM, which was the upper limit of testing condition in other reports. In the range of 1-80 mM L-arginine, the SaADC showed the K_m, k_cat, K_i, and k_cat/K_m values of 72.99 ± 6.45 mM, 42.88 ± 2.63 s^-1, 20.56 ± 2.18 mM, and 0.59 s/mM, respectively, which were much higher than the K_m (14.55 ± 1.45 mM) and k_cat (12.62 ± 0.68 s^-1) value obtained by assaying at 1-50 mM L-arginine without considering substrate inhibition. Both the k_cat values of SaADC with and without substrate inhibition are the highest ones to the best of our knowledge. This provides a reference for the study of substrate inhibition of ADCs.