Reduction of disulphide bonds in human haptoglobin 2-1

Gradual reduction of disulphide bonds in human haptoglobin, type 2-1, was carried out either by the use of sodium borohydride or 2-mercaptoethanol, newly exposed sulphydryl groups as determined by the Ellman's reagent and by the incorporation of [(14) C] acetamide, respectively. Cleavage of disulphide bonds resulted in the formation of a number of intermediates, separated in polyacrylamide gel electrophoresis, with sulphydryl groups blocked by the radioactive label. On the basis of molecular mass determinations, subunit composition of intermediates, was postulated. The ability of haptoglobin to form an active peroxidase-like complex with hemoglobin depended to a considerable extent on the presence of intact disulphide bonds. On the contrary,throughout the course of reduction of inter- and intrachain disulphides, antigenic reactivity was found to remain unchanged.