Amino Acid Sequences Surrounding the Sulfhydryl Groups of the A Protein Subunit of the Escherichia coli Tryptophan Synthetase

The following sequences of amino acids surrounding the three sulfhydryl groups of the Escherichia coli tryptophan synthetase A protein were established: Sequence I, Gly-Ile-Asp-Glu-Phe-Tyr-Ala-Gln-Cys-Glu-Lys-Val-Gly-Val-Asp-Ser-Val-Leu-Val-Ala-Asp-Val-Gln-Glu-Ser-Ala-Pro-Phe-Arg; Sequence II, Arg-Ala-Phe-Ala-Ala-Gly-Val-Thr-Pro-Ala-Gln-Cys-Phe-Glu-Met-Leu-Ala-Leu-Ile-Arg; Sequence III, Arg-His-Asn-Val-Ala-Pro-Ile-Phe-Ile-Cys-Pro-Pro-Asn-Ala-Asp-Asp-Asp-Leu-Leu-Arg.... Conventional methods of sequence analysis were used with performic acid-oxidized protein and S-β-aminoethyl protein prepared by reaction with cyclic 14C-ethyleneimine. Studies on the chemical modification of the A protein with ethyleneimine indicated that a net of 2 cysteine residues are essential for enzymatic activity, supporting the results of previous studies with iodoacetate.