The sub‐picomolar Cu2+ affinity of human serum albumin

The apparent affinity of human serum albumin (HSA) for divalent copper has long been the subject of great interest, due to its presumed role as the major Cu(2+) -binding ligand in blood and cerebrospinal fluid. Using a combination of electronic absorption, circular dichroism and room-temperature electron paramagnetic resonance spectroscopies, together with potentiometric titrations, we competed the tripeptide GGH against HSA to reveal a conditional binding constant of log (c) K Cu Cu ( HSA ) =13.02+/-0.05 at pH 7.4. This rigorously determined value of the Cu(2+) affinity has important implications for understanding the extracellular distribution of copper.