T2r+ Bacteriophage-induced Enzymes

T2r+ bacteriophage-induced deoxycytidylate deaminase was purified over 3000-fold to homogeneity as revealed by polyacrylamide gel electrophoresis, immunodiffusion, and sedimentation velocity measurements. In the latter case, a value of s20,w = 6.05 ± 0.05 was obtained. Antibody to the T2r+ bacteriophage-induced enzyme cross-reacted with T4r+ bacteriophage-induced deoxycytidylate deaminase, but not with the chick embryo deaminase. Amino acid analyses revealed the enzyme to have a high sulfhydryl content (approximately 50 —SH per mole) and a relatively low methionine content (approximately 10 to 13 per mole). Although active at pH 6.0 in the absence of deoxycytidine 5'-triphosphate, the pH optimum of the deaminase was shifted from 5.3 to 8.3 in the presence of this nucleotide. The quantity of deoxycytidine 5'-triphosphate required to activate the reaction by 50% increased with the pH as did the sigmoidal nature of the activation. A similar response was obtained with 5-hydroxymethyl deoxycytidine 5'-triphosphate, but in this case the effects were even more striking. The ratio of deoxythymidine 5'-triphosphate to 5-hydroxymethyl deoxycytidine 5'-triphosphate, necessary to achieve a 50% inhibition, was independent of pH, but the ratio decreased sharply as the pH was raised when deoxycytidine 5'-triphosphate was substituted for the hydroxymethyl derivative. The degree of inhibition effected by deoxythymidine 5'-triphosphate appears to be a function of the positive effector response to pH. When compared with deoxycytidine 5'-triphosphate, 5-hydroxymethyl deoxycytidine 5'-triphosphate is more susceptible to inhibition by deoxythymidine 5'-triphosphate. This effect is not unreasonable in view of the fact that 5-hydroxymethyl deoxycytidine 5'-triphosphate is a more immediate precursor of T-even bacteriophage deoxyribonucleic acid than is deoxycytidine 5'-triphosphate.