Interaction between low-affinity cupric ion and human methemoglobin.

Human hemoglobin has been shown to contain a high- as well as a low-affinity binding site for cupric ion on each of its constitutent beta chains. The copper that is bound to the low-affinity site has been implicated in the selective oxidation of the beta hemes. In the present work a low-affinity binding site for cupric ion has been located within 10 A of the heme iron in human hemoglobin. It is suggested that the proximal histidine is involved in the binding of copper at this site and that it participates in the oxidation of heme iron and reduction of cupric ion.