Schematic map of the haptoglobin subunits and truncated haptoglobin mutants.

Native haptoglobin (hatched) is made as a single polypeptide and then cleaved into an α- and a β-chain joined by disulfide bonds to form a haptoglobin monomer. The 2 alleles for haptoglobin differ only in their α-subunit. The RHp constructs were made as described in “Materials and methods” and correspond to the amino acids of the β or α chain, as shown. RHp 1 is the entire β-chain. RHp2 to RHp4 are truncated mutants of the β-chain. RHp5 is the α-chain from the 2 allele, and RHp6 is the α-chain from the 1 allele.