Cytidine deaminase activity in Penicillium politans NRC-510

Cell-free extracts of nitrate-grown Penicillium politans NRC-510 catalyzes the hydrolytic deamination of cytidine to uridine. Uridine was chromatographically identified in cell-free extracts. The enzyme exhibited optimum pH and temperature activities at 6.5 and 80 degrees C respectively. Thermal stability experiments indicated that the enzyme restored its activity at 80 degrees C for at least 60 minutes. When cell-free extracts were incubated at 90 degrees C for 5 minutes enzyme activity was inhibited by about 33%. The involvement of sulfhydryl group(s) in the catalytic site of the enzyme was shown. HgCl2 (5 x 10(-3) M) and CuSO4 (10(-2) M) caused a complete inhibition of enzyme activity. Ethylene diamine tetraacetate at a concentration of 5 x 10(-3) M and 10(-2) M inhibited the enzyme as well. Whereas, MgCl2, CoSO2 and MnCl2 had a remarkable activating effect. Dialysis of the cell-free extracts resulted to an increase in enzyme activity by about 30%. To our knowledge the thermophilic nature of the cytidine deaminase of P. politans NRC-510 is unique.