The Amino Acid Sequence of the Tryptophan-Containing Subunit (?-Subunit) of Bovine Brain S-100 Protein

Abstract: The tryptophan‐containing subunit (α‐subunit) of bovine brain S‐100 protein was purified from a S ‐aminoethyl derivative of S‐100a protein, and its amino acid sequence was determined. The α‐subunit contained 93 residues, including one tryptophan, and had a molecular weight of 10,400. The sequence shows an extensive homology (58% identity) to the sequence of another “tryptophan‐free” subunit (β‐subunit) found in both S‐100a and S‐100b protein, and has a calcium binding site characteristic of the “E‐F hand” proteins, such as calmodulin or troponin C. The tryptophan residue is located at position 90 which is presumably adjacent to the C‐terminal end of the α‐helix following the calcium binding loop, and thus appears likely to serve as a specific probe in structure‐function studies of S‐100a protein.