The Purification and Properties of Cytidine Deaminase from Escherichia coli

Abstract

Cytidine deaminase [cytidine aminohydrolase, EC 3.5.4.5] has been purified about 25-fold from the osmotic shock fluid of a constitutive mutant of Escherjchia coli. The molecular weight of the enzyme is approximately 54,000. High concentrations of urea reversibly inactivate cytidine deaminase activity, but do not cause the dissociation of the enzyme to smaller subunits. The enzyme catalyzes the deamination of various amino-pyrimidine nucleosides with activity in the following order: deoxycytidine, fluorodeoxycytidine, 5-methyl- deoxycytidine, cytidine, and cytosine arabinoside. All deoxy- and ribonucleosides were found to inhibit the activity. Various heavy metal ions inhibit the enzyme, but sulfhydryl reagents including p-chloromercuribenzoate show no effect.