Complete amino acid sequence of an allosteric enzyme, T2 bacteriophage deoxycytidylate deaminase

The amino acid sequence of deoxycytidylate deaminase isolated from T2 phage-infected Escherichia coli has been determined. The enzyme is a hexamer, consisting of identical polypeptide subunits, each composed of 188 amino acids with a calculated Mr = 20,560. The primary structure was established by automatic Edman degradation of the intact carboxymethylated protein and of peptides derived from the protein by cleavage with cyanogen bromide, trypsin, chymotrypsin, the Staphylococcus aureus V8 protease, and 2-(2-nitrophenylsulfenyl)-3-methyl-3-bromoindolenine. Knowledge of the primary structure of deoxycytidylate deaminase should aid in determining the allosteric binding site of the negative effector, dTTP, recently reported (Maley, F., and Maley, G.F. (1982) J. Biol. Chem. 257, 11876-11878), and eventually that of the enzyme's positive regulator, dCTP, as well as its substrate. The deaminase has been crystallized through the use of polyethylene glycol; a scanning electron micrograph is presented.