Abstract
Cytosine deaminase (EC 3.5.4.1) was extracted from commercial compressed bakers' yeast and purified to an almost homogeneous state. The enzyme activity was more than 200 U/mg of protein, which was several times higher than reported before. The molecular weight was 41, 000 by gel permeation. The pi was at pH 4.7. 5-Fluorocytosine, 5-methylcytosine, and creatinine were other substrates for the enzyme. An experiment with inhibitors suggested that the enzyme was an SH-enzyme. The enzyme was unstable to heat, with a half-life of about 0.5 hr at 37°C. Characteristics of the enzyme, especially its substrate specificity, were compared with those reported earlier for other cytosine deaminases from bacteria and a mold.
