Aspergillus oryzae acetamidase catalyzes degradation of ethyl carbamate

Urethanase (EC 3.5.1.75) catalyzes the hydrolysis of ethyl carbamate (EC) to ethanol, carbon dioxide, and ammonia. From our recent study, we expected that an acetamidase encoded by amdS of Aspergillus oryzae may catalyze the degradation of EC because it is homologous with a Candida parapsilosis urethanase (CPUTNase) recently identified. Urethanase is a prospective candidate to reduce EC in alcoholic beverages, but knowledge of this enzyme is very limited. Recombinant AmdS was expressed to study its enzymatic properties. Purified AmdS was identified as a homo-tetramer consisting of four 60 kDa units and exhibited urethanase activity. In a 20% ethanol solution, AmdS had 65% activity compared with a solution without ethanol. Residual activity after 18 h indicated that AmdS was stable in 0%–40% ethanol solutions. The optimum temperature of AmdS was 40 °C. This enzyme showed urethanase activity at pH 6.4–9.6 and exhibited its highest activity at pH 9.6. The Km value of AmdS for EC was 8.2 mM, similar to the Km value (7.6 mM) of CPUTNase. AmdS showed activity not only for EC and acetamide but also other amide compounds. In this study, we investigated the enzymatic properties of AmdS that was identified as acetamidase and showed that an amidase can be an enzymatic candidate that degrades EC.