The antileukemic activity of cytosine arabinoside (ara-C) is due to its conversion in the cell successively to the 5'-mono-, di-, and triphosphates [i]. This reaction competes with the catabolic deactivation of ara-C by deamination in the presence of cytidine deaminase [i]. Thus, the conversion of ara-C to its 5'-monophosphate (ara-CMP) is of crucial importance for the occurrence of physiological activity. This is the main reason for the interest of ...