Haemoglobin binding with haptoglobin. Localization of the haptoglobin-binding site on the alpha-chain of human haemoglobin.

A synthetic approach was employed to identify the haptoglobin-binding site on the alpha-chain of human haemoglobin. This approach cosists of the synthesis of a series of consecutive overlapping peptides that, together, systematically represent the entire protein chain. Fourteen peptides were synthesized (alpha 1-15, alpha 11-25, alpha 21-35, alpha 31-45, alpha 41-55, alpha 51-65, alpha 61-75, alpha 71-85, alpha 81-95, alpha 91-105, alpha 101-115, alpha 111-125, alpha 121-135 and alpha 131-141), and their ability bind human haptoglobin was studied, Only peptide alpha 121-135 bound haptoglobin significantly. On this basis we conclude that the haptoglobin-binding site on the alpha-chain of haemoglobin resides within, but does not necessarily encompass all of, the region alpha 121-135.