New urethanase from the yeast Candida parapsilosis.

ABSTRACT

Urethanase (EC 3.5.1.75) is an effective enzyme for removing ethyl carbamate (EC) present in alcoholic beverages. However, urethanase is not well studied and has not yet been developed for practical use. In this study, we report a new urethanase (CPUTNase) from the yeast Candida parapsilosis. Because C. parapsilosis can assimilate EC as its sole nitrogen source, the enzyme was extracted from yeast cells and purified using ion-exchange chromatography. The CPUTNase was estimated as a homotetramer comprising four units of a 61.7 kDa protein. In a 20% ethanol solution, CPUTNase had 73% activity compared with a solution without ethanol. Residual activity after 18 h indicated that CPUTNase was stable in 0%-40% ethanol solutions. The optimum temperature of CPUTNase was 43°C. This enzyme showed urethanase activity at pH 5.5-10.0 and exhibited its highest activity at pH 10. The gene of CPUTNase was identified, and a recombinant enzyme was expressed in the yeast Saccharomyces cerevisiae. Characteristics of recombinant CPUTNase were identical to the native enzyme. The putative amino acid sequence indicated that CPUTNase was an amidase family protein. Further, substrate specificity supported this sequence analysis because CPUTNase showed higher activities toward amide compounds. These results suggest that amidase could be a candidate for urethanase. We discovered a new enzyme and investigated its enzymatic characteristics, sequence, and recombinant CPUTNase expression. These results contribute to a further understanding of urethanase.