Studies on haptoglobin binding to concanavalin A.

Ascitic fluid haptoglobins 1-1, 2-1 and 2-2 and their tryptic glycopeptides were fractionated by affinity chromatography on Con A-Sepharose. Three peaks were obtained, corresponding to non-binding, weakly binding and strongly binding fractions. Concanavalin A-non-binding and concanavalin A-binding fractions of haptoglobin and of glycopeptide III 2-2 consisted of a series of polymers with increasing molecular mass, except for the non-binding fraction of glycopeptide III 1-1. After reduction there was no difference between the subunit composition of the glycopeptides and their concanavalin A fraction. Concanavalin A-non-binding fractions from haptoglobin 2-1 and glycopeptides III 1-1 and III 2-2 did not form an active complex with hemoglobin and, in crossed immunodiffusion, showed a reaction of partial identity with haptoglobin 2-1, glycopeptides III 1-1, III 2-2 and their concanavalin A-binding fractions. Concanavalin A-binding fractions of the above preparations exhibited with hemoglobin higher peroxidase activity than before their separation on Con A-Sepharose and immunodiffusion gave a reaction of identity among themselves and with unfractionated preparations. The concanavalin A-binding glycopeptide III is the biologically active part of the haptoglobin beta-chain.