Urea amidolyase of Candida utilis : Characterization of the urea cleavage reactions

Abstract

Evidence is presented that the enzymes catalyzing the three reactions involved in urea cleavage in Candida utilis, biotin carboxylation, urea carboxylation, and allophanate hydrolysis occur as a complex of enzymes. The allophanatehydrolyzing activity could not be separated from the urea-cleaving activity using common methods of protein purification. Further, urea cleavage and allophanate hydrolysis activities are induced coordinately in cells grown on various nitrogen sources.The reactions involved in urea cleavage can be distinguished from one another on the basis of their sensitivities to (a) heat, (b) pH, and (c) chemical inhibitors. Evidence is presented for the product of the first reaction in urea cleavage, biotin carboxylation. Production of carboxylated enzyme is ATP dependent and avidin sensitive. Carboxylated enzyme is not observed in the presence of 1 mM urea.