The amino acid sequence and copper(II)-binding properties of peptide (1-24) of bovine serum albumin.

1. The amino acid sequence of peptide (1-24) obtained from limited peptic digestion of bovine serum albumin has been determined from characterization of its tryptic and chymotryptic peptides. The 3 histidyl residues have been shown to occupy positions 3,9, and 18. 2. Hydrogen ion titration of this peptide with and without copper ions indicates that at neutral pH there are two copper(binding sites of appreciable strength on the peptide. Of these, one site binds copper(I1) ions strongly while the other binds copper ions more weakly. In addition to the differences observed by titration, marked differences between the sites are apparent from absorption spectra, circular dichroism spectra, and optical rotatory dispersion spectra. 3. Since the peptide binds only 2 copper(I1) ions strongly, all 3 histidyl residues do not act with comparable effect in separate binding sites. 4. The site which binds the 1st copper(I1) ion has been shown by hydrogen ion titration, absorption spectra, circular dichroism spectra, and optical rotatory dispersion spectra to have properties compatible with previous suggestions that it is composed of the a-amino nitrogen, the imidazole nitrogen from the histidine in position 3, and the 2 intervening peptide bond nitrogen atoms. 5. Occupancy of either site by copper(I1) leads to absorption in several circular dichroic bands. In addition to the several bands in the visible and near ultraviolet that have some similarities to those observed previously with complexes of small peptides, it has been possible to resolve two bands of opposite sign centered near 300 to 308 rnp and 270 to 275