The S100-b protein: tyrosine residues do not exhibit an abnormal fluorescence spectrum

The beta subunit of the bovine brain S100-b protein (beta beta) lacks tryptophyl residue but contains one tyrosine. Our experiments show that this protein is characterized by a typical tyrosine fluorescence spectrum, with a maximum at 303 nm. Identical fluorescence properties were found for the rat brain S100-b protein. Comparison with the fluorescence spectrum of the bovine brain S100-a' protein (alpha'beta), which contains a tryptophan residue in the alpha' subunit, enables us to demonstrate that the recent report describing an abnormal fluorescence spectrum for the bovine brain S100-b protein may result from a contamination of the S100-b by the S100-a' protein.