Mouse Kidney Cytidine Deaminase

A nucleoside aminohydrolase was prepared in 60-fold relative purity from the nonparticulate fraction of mouse kidney by denaturation at 60", fractionation with (NH&S04, treatment with alumina gel Cr (pH 7.5), and dialysis in 0.02 M acetate buffer (pH 4.5).The' optimal pH was 6.5.Cytidine, deoxycytidine, and I-/3-D-arabinofuranosylcytosine were deaminated, and the respective K, values were 7.53 x 10-5, 7.25 x 10d5, and 1.01 x 10W3.Divalent metals were not required for activity.Inhibition by p-chloromercuribenzoate indicated participation of sulfhydryl groups.The use of l-@-n-arabinofuranosylcytosine in cancer chemotherapy (l-3) has directed considerable interest to a cytosine nucleoside deaminase that apparently converts the active compound to the inactive met'abolite, I-fl-n-arabinofuranosyluracil (4).Camiener and Smith (4) have shown that homogenates of a variety of tissues from man and various animal species are capable of deaminating ara-Cl as well as deaminating cytidine to uridine.It was considered that a specific deaminase might exist for ara-C and possibly measures could be taken to restrict this aspect of its catabolism.Creasey (5) used a partially purified deaminase preparation obtained from mouse kidney and showed that approximately 6% of the ara-C was deaminated as compared with cytidine, although 5-halogenated derivatives of cytidine were deaminated more rapidly than the parent compound.Recently, Wisdom and Orsi (6) isolated a cytidine aminohydrolase from the soluble fraction of sheep liver.The substrate specificity was similar to that of the mouse kidney enzyme reported by Creasey.Wang (7) attempted purification of a cytosine nucleoside deaminase from Escherichia coli.However, this enzyme had a greater affinity for deoxycytidine than for cytidine.