Abstracts of Papers Presented at the Third International Complement Workshop, Harvard Medical School, Boston, Massachusetts, June 3–5, 1968

Reduction of partially purified IgM hemolysin (A) in solution, or bound to sheep erythrocytes (EA), is accompanied by loss of complement (C′)-fixing activity. C′-fixing activity is not recovered under mild oxidizing conditions. After reaction of EA with the jack bean lectin, concanavalin A, C′-fixing activity of the hemolysin can be destroyed by reduction and recovered by mild oxidation. C′-fixing activity of the reduced and re-oxidized products is determined after dissociation of concanavalin A from the complex using methyl-α-D glucoside. Reversibility of reduction after reaction of A with both Forssman antigen on the sheep erythrocytes and concanavalin A is interpreted as being due to increased rigidity of A under conditions where at least part of the FAB and FC portions of the molecule are complexed. The sulfhydryl groups formed on reduction are thus constrained and on re-oxidation form the same disulfide bonds found in the native molecule.