Haptoglobin-hemoglobin complex. Subunit interaction probed by cross-linking.

Haptoglobin-hemoglobin complex has been cross-linked using the bifunctional reagent 1,5-difluoro-2,4-dinitrobenzene. Sodium dodecyl sulfate-acrylamide gel electrophoresis indicated that specific cross-linking was obtained between haptoglobin H chain and a hemoglobin chain. The cross-linked complex was reduced and denatured, and the cross-linked subunits were separated from the unreacted haptoglobin and hemoglobin chains by molecular sieve chromatography. Peptide analysis on the purified cross-linked subunits showed that haptoglobin H chain was cross-linked to hemoglobin beta chain only. This result indicates that the H and beta chains are in close proximity in the haptoglobin-hemoglobin complex.