Abstract
Abstract A 24-residue peptide, called the fragment, has been isolated from a peptic digest of bovine serum albumin. This peptide has the same terminal sequence, Asp-Thr-, as does bovine serum albumin, and will similarly bind a single ion of copper(II) at its terminal α-amino group. Spectral and titrimetric data are reported which suggest that the Cu(II)-binding site for both albumin and peptide is a chelate locus involving multiple nitrogenous ligands in the neutral pH range. Addition of copper(II) to the peptide decreases the slope of its titration curve in the pH range, 6 to 7, and decreases its catalytic effect on the hydrolysis of p-nitrophenyl acetate. These effects lead to the proposal that a histidyl residue occupies position 3 in the peptide chain and that the unique binding site for Cu(II) in both the Asp fragment and intact albumin is the amino-terminal sequence, Asp-Thr-His-. The bulk of the albumin molecule has relatively little influence on the properties of this site.
Highlights
Cu(II)-binding site for both albumin and peptide is a chelate locus involving multiple nitrogenous ligands in the neutral
Tests of the rate of hydrolysis of p-nitrophenyl acetate were by the procedure of Koltun, Fried, and Gurd [7]
Multiple protons are displaced from this site by the copper ion in the neutral pH range, and the resulting configuration, owing to multiple ligands to nitrogen atoms, produces the absorption band at 525 rnp which is not seen with other
Summary
Proton release on addition of CuClz was determined by back titration to the original pH with 0.2 N NaOH.pH was measured with a Radiometer model 22 pH meter at25”, standardized at pH 4.01 and 7.00. The specimen was brought to pH 7.0 in a total volume of 2.0 ml of 0.04
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