The Purification and Properties of Cytidine Aminohydrolase from Sheep Liver.

Cytidine aminohydrolase was purified about 280-fold with an overall 8% yield from the cytoplasmic fraction of sheep liver cells by the use of protamine sulphate precipitation, salt fractionation using trisodium citrate, acidification and chromatography on DEAE- and CM-celluloses. The enzyme catalyses the deamination of several aminopyrimidine nucleosides. Its pH optimum occurred at 5.0 and it was relatively acid and heat stable. The high sensitivity of the enzyme to compounds known to react with sulphydryl groups and the presence of a substrate- binding group of pKa 9.2 in the enzyme suggests that a sulphydryl group may be important in the catalytic process. dTTP and dUTP were found to inhibit and dCTP to activate the enzyme respectively. The complex type of inhibition produced by dTTP indicates that this amino- hydrolase may have a regulatory role similar to that of dCMP aminohydrolase. [ABSTRACT FROM AUTHOR]