The Half-Molecule of Haptoglobin: Studies on the Product Obtained by the Selective Cleavage of a Haptoglobin Disulfide

A disulfide of haptoglobin 1-1 has been selectively cleaved using sodium sulfite and p-chloro-mercurisulfonate. The reaction product (half-haptoglobin) could be separated from haptoglobin by gel electrophoresis in urea or sodium dodecyl sulfate, and its molecular weight was one-half that of native haptoglobin 1-1. When the sulfite cleavage reaction was performed on haptoglobin 2-2 the haptoglobin polymers were broken down. Isolation of the S-sulfocysteine-containing peptide revealed that the disulfide bond broken in the formation of half-haptoglobin was the 21α-21α disulfide. This conclusion was confirmed by analysis of the cyanogen bromide fragments from half-haptoglobin and by a performic acid diagonal analysis of peptic peptides obtained from half-haptoglobin.