The Sequence of Amino Acid Residues around the Sulfhydryl Group at the Active Site of Streptococcal Proteinase.

The present communication describes the elucidation of the sequence of amino acid residues around the single half-cysteinyl residue (Liu, Neumann, Elliott, Moore, and Stein (1)) of the proteinase derived from the zymogen produced by Group A hemolytic streptococci (Elliott (2)). This -SH group is essential for the proteolytic activity of the reduced enzyme; therefore, as a working hypothesis, the cysteine residue may be considered to be at the active site of the cat,alyst. The sulfhydryl group in the enzyme has been labeled with iodoacetic-l-r4C acid, the labeled protein has been hydrolyzed with trypsin, a ‘%-containing peptide of 27 amino acid residues has been isolated, and its struct’ure determined.