Di-, tri-, and tetrapeptide sequences in haptoglobin. Contribution to understanding of haptoglobin structure.

Amino acid sequences of haptoglobin and 11 proteins related and unrelated to haptoglobin were resolved into overlapping di-, tri-, and tetrapeptides. Comparison of the obtained peptides confirmed the existence of homology between haptoglobin and the family of serine proteases. The homology with light chain of immunoglobulins was relatively weak. A surprising similarity with concanavalin A was found. Tetrapeptide beta-turns (chain reversals), characterized by Chou & Fasman (1977, J. Mol. Biol., 115, 135-175) were compared with similar structures in light (alpha) and heavy (beta) subunits of haptoglobin.