The Amino Acid Sequence of the A Protein (α Subunit) of the Tryptophan Synthetase of Escherichia coli

The isolation and partial sequences of 48 chymotryptic peptides of the tryptophan synthetase A protein (α subunit) of Escherichia coli are described. Some 17 peptic and 12 tryptic peptides isolated from the chymotrypsin-resistant core fraction are also described. Together, they account for 254 of the 267 amino acid residues in the A protein. Of the 23 overlapping peptides required to link the 24 nonoverlapping tryptic peptides comprising the A protein, 22 overlaps can be recognized. However, because of the abundance of single residue overlaps, many of these cannot be defined with certainty. The assignment of overlaps and the nature of the chymotryptic core are discussed with reference to the proposed structure of the A protein.