الملخص

ABSTRACT Cytosine deaminase (EC.3.5.4.1) activity and properties was determined in the extract of the free living ciliata Tetrahymena pyriformis grown in proteose peptone medium. The optimum conditions for the enzyme activity was also determined and it was found that the highest activity was obtained from the reaction mixture containing 300 M of Tris-HCl buffer at pH 7.2 containing 3 μM of cytosine as a substrate and a concentration of enzyme extract equal to 250 g at 35C for 10 min. Under the optimum conditions, the specific activity was found to be 42.23±2.3 M of cytosine deaminated per min per mg protein in the supernatant of Tetrahymena pyriformis extracts compared with 20.08 ± 1.0 M of cytosine deaminated per min per mg protein.