Purification of cytidine deaminase from chicken liver

Cytidine deaminase (cytidine aminohydrolase, EC 3.5.4.5) from chicken liver has been obtained in pure form through a rapid procedure consisting of organic solvent precipitation, heat treatment, anionic-exchange chromatography, hydrophobic interaction chromatography followed by two rapid chromatographies using an FPLC system. The final preparation is pure but shows microheterogeneity as judged by a single band obtained by SDS-gel electrophoresis and a series of superimposed active bands obtained on native gel electrophoresis and gel isoelectrofocusing. The native protein molecular weight determined by gel filtration is 50,000. SDS-gel electrophoresis experiments conducted in the presence and in the absence of reducing agents, suggest an oligomeric structure of four apparently identical subunits of 12,000 molecular weight. The absorption spectrum of the native protein reveals a maximum at 278 nm and a minimum at 261 nm with a small shoulder at 285 nm. The isoelectric point has an average value around pH 4.45.