Purification and properties of cytosine deaminase from Aspergillus fumigatus

Cytosine deaminase (EC 3.5.4.1) from Aspergillus fumigatus IFO 5840, which is the first cytosine deaminase to be found in a mould, was purified 150-fold with an overall yield of 0.75%, to homogeneity judging from disc and SDS-polyacrylamide gel electrophoresis. The enzyme was a monomer of 32 kDa. Besides cytosine, the enzyme stoichiometrically deaminated 5-methylcytosine and 5-fluorocytosine: the activity toward them was 100:28:43, and the apparent K m values for them were 2, 36, and 6.5 mM, respectively. The enzyme had a pH optimum at around pH 7 and temperature optimum at 35°C. The enzyme activity was inhibited by heavy metal ions such as Fe 2+ , Cu 2+ , Hg 2+ , and Pb 2+ at 0.1 mM, and by p -chloromercuribenzoate, o -phenanthroline, ATP, and UTP at 1 mM.