Kinetic mechanism of copper(II) transfer between the native sequence peptide representing the copper(II)-transport site of human serum albumin and L-histidine

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Abstract
The kinetics for Cu(II)-transfer reaction of the native sequence tripeptide, L-aspartyl-L-alanyl-L-histidine-N-methyl amide (AAHNMA), representing the Cu(II)-transport site of human serum albumin (HSA), and L-histidine (L-His) was studied in the forward and reverse reactions in a pH range 6.5–10.0 at I = 0.2 and 25°. For the Cu(II)-transfer from Cu(II)-L-His2 to native sequence peptide, the rate-determining step is a bond formation between Cu(II) and peptide nitrogen to form CuH−1AB from CuAB by deprotonation of peptide nitrogen atom, where A and B denote the anionic forms of AAHNMA and L-His, respectively. For the Cu(II)-transfer reaction from Cu(II)–peptide to L-His, the rate-determining step is a bond breaking between Cu(II) and peptide nitrogen to form CuAB fromCuH−1AB by protonation to a peptide nitrogen. The effect of carboxyl group of aspartyl residue in the native sequence peptide on the kinetic and equilibrium constants are discussed.