Purification and properties of the inducible enzyme cyanase

Cyanase (cyanate hydrolase EC 3.5.5.3) has been purified 270-fold to a high state of purity from Escherichia coli B. The native enzyme has a molecular weight of approximately 150 000 as estimated by sucrose density gradient centrifugation and gel-filtration chromatography on Bio-Gel P-300. The enzyme is an oligomer composed of apparently identical subunits which have a molecular weight of approximately 15 000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Amino acid analyses showed that the enzyme contains no tryptophan and a single histidine residue, based on a subunit molecular weight of 14 661. Catalytic hydrolysis of cyanate was found to be dependent on the patience of bicarbonate and to be affected by ionic strength. The concentration of bicarbonate required to give half-maximal activity in the presence of 2 mM potassium cyanate was 0.1 mM. The apparent Km for cyanate in the presence of 3 mM bicarbonate is 0.6 mM. The initial product of the reaction is carbamate (or a related, unstable compound and/or carbamate precursor) which subsequently decomposes to ammonia and bicarbonate.