A new investigation of copper(II)-serine, copper(II)-histidine-serine, copper(II)-asparagine, and copper(II)-histidine-asparagine equilibria under physiological conditions, and implications for simulation models relative to blood plasma

Abstract

Some years ago, the application of computer modeling to metal speciation in biofluids was questioned based on the discrepancy between the simulated distribution of copper(II) in blood plasma and related experimental results obtained by Neumann and Sass-Kortsak in reconstituted serum. A recent investigation of the relevant copper(II)-amino acid equilibria reconciled these conflicting data, confirming that the reliability of computer models crucially depends on the data on which they are based. Since then, however, some of the constants of the copper-serine system used in that study have been suspected to be overestimated. This work thus reports the redetermination of copper-serine and copper-histidine-serine formation constants under physiological conditions. In addition, serine being close to asparagine in Neumann and Sass-Kortsak's classification, copper-asparagine and copper-histidine-asparagine equilibria have also been reinvestigated. For asparagine complexes, former constants have been basically confirmed. In contrast, all constants relative to serine have effectively been found lower than the previous ones. The effects of these new data on the stimulated distribution of plasma copper are only minor, but a better agreement is observed relative to Neumann and Sass-Kortsak's models in reconstituted serum.