Copper(II)-binding equilibria in human blood.

ABSTRACT: It has been reported that Cu(II) ions in human blood are bound mainly to serum albumin (HSA), ceruloplasmin (CP), alpha-2-macroglobulin (?2M) and His, however, data for ?2M are very limited and the thermodynamics and kinetics of the copper distribution are not known. We have applied a new LC-ICP MS-based approach for direct determination of Cu(II)-binding affinities of HSA, CP and ?2M in the presence of competing Cu(II)-binding reference ligands including His. The ligands affected both the rate of metal release from Cu•HSA complex and the value of K_D. Slow release and K_D?=?0.90 pM was observed with nitrilotriacetic acid (NTA), whereas His showed fast release and substantially lower K_D?=?34.7 fM (50?mM HEPES, 50?mM NaCl, pH 7.4), which was explained with formation of ternary His•Cu•HSA complex. High mM concentrations of EDTA were not able to elicit metal release from metallated CP at pH 7.4 and therefore it was impossible to determine the K_D value for CP. In contrast to earlier inconclusive evidence, we show that ?2M does not bind Cu(II) ions. In the human blood serum ~75% of Cu(II) ions are in a nonexchangeable manner bound to CP and the rest exchangeable copper is in an equilibrium between HSA (~25%) and Cu(II)-His-Xaa ternary complexes (~0.2%).

SUBMITTER: Kirsipuu T 

PROVIDER: S-EPMC7105473 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature