The Haptoglobin binding to Apolipoprotein A-I: Influence of Hemoglobin and Concanavalin A.

Haptoglobin (Hp) can be purified by affinity chromatography using hemoglobin(Hb)-linked Sepharose. Elution with 8 M urea is generally performed, resulting in Hp heavy contamination by the apolipoprotein AI (ApoAI), and partial loss of Hb binding activity. Hp, separated from ApoAI, was recovered by elution with glycine-HCl at pH 3. Complexes of the isolated protein with Hb or ApoAI were detected by enzyme-linked immunosorbent assay (ELISA). Competition between the two ligands in their interaction with Hp was observed. Concanavalin A (ConA), which binds the Hp carbohydrate chains, did not influence the Hp binding to ApoAI. The results suggest that changes in the plasma level of ApoAI or Hb affect the Hp role in regulating the cholesterol reverse transport or preventing Hb-dependent oxidative damages.