title: Cytidine deaminase activity of human normal and malignant lymphoid cells.
abstract: Cytidine deaminase activity was determined by a radioisotopic assay in extracts of peripheral blood mononuclear cells of normal individuals and of patients with acute lymphoblastic leukaemia. The normal enzyme activity had a broad pH optimum between pH 6.5 and 8.0; apparent Km values for cytidine and deoxycytidine were 3.6 +/- 0.6 mumol/l and 26.5 +/- 3.5 mumol/l, respectively; the activity was resistant to heat inactivation; of the various effectors tested, only uridine, deoxyuridine and tetrahydroxyuridine had inhibitory effects. Cytidine deaminase activity was markedly decreased in lymphoblasts of patients with acute lymphoblastic leukaemia; enzyme activity was related to the percentage of circulating blast cells, and not to the clinical, cytological or immunological characters of the leukaemia.
mesh_terms: D001402:B-Lymphocytes / Q000201:enzymology*; D003564:Cytidine Deaminase / Q000037:antagonists & inhibitors / Q000097:blood*; D004355:Drug Stability; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007945:Leukemia, Lymphoid / Q000201:enzymology*; D009700:Nucleoside Deaminases / Q000097:blood*; D012016:Reference Values; D013601:T-Lymphocytes / Q000201:enzymology*
chemical_list: D009700:Nucleoside Deaminases; D003564:Cytidine Deaminase