Copper and nickel binding to canine serum albumin. A circular dichroism study

The binding of copper and nickel to canine serum albumin has been studied using circular dichroism. In the 320-700 nm region, only a single positive extremum was observed at about 664-667.5 nm for copper bound to canine serum albumin. The intensity of this extremum was found to increase until a Cu2+/albumin molar ratio of 3 was reached. Further addition of Cu2+ led to a decrease in ellipticity. The absence of any extrema in the 560-570 and 480-510 nm regions showed that histidines were not involved in copper binding to canine albumin. In the case of nickel, initial binding was found to take place at the N-terminal tripeptide. At higher nickel to albumin molar ratios, circular dichroism spectra indicated the presence sulfur containing ligands but showed no evidence for the involvement of histidines. Canine serum albumin was found to bind six or more Cu2+ and Ni2+ ions with affinities that are lower than for human or bovine serum albumin.