Effect of mercaptans and other agents on the human complement component β1C-globulin

Immunoelectrophoretic analyses and complement titrations of whole human serum show that a number of physical, chemical and immunological agents affect the β_1C/β_1A-globulin system which is considered to represent the third component of complement (C′₃). The transformation from β_1C-globulin to β_1A-globulin is the normal result of ageing, while antigen-antibody complexes, polylysine, hydrazine and cobra venom accelerate this change. In addition, α-globulin fragments of β_1A-globulin appear after interaction of normal sera with antigen-antibody complexes, treatment with cobra venom, and by storage under nitrogen in glass tubes or in polyethylene containers. Similar α-fragments are seen in the aged sera of some patients with glomerulonephritis or renal allografts. With prolonged storage these α-fragments can reform β_1A-globulin. On the other hand, 2-mercaptoethanol and penicillamine produce complete dissolution of β_1C-globulin into rapidly migrating, poorly defined fragments in the α-globulin and albumin regions, and transform β_1A-globulin into a stable β₂-globulin. The reduced fragments of β_1C-globulin, if not alkylated, can subsequently form the β₂-globulin, but not the β_1A-globulin. These results indicate that β_1C-globulin is composed of several subunits, some of which are joined by disulphide bonds, but that the α-globulin fragments seen in some pathological sera are not a result of disulphide bond reduction.