The properties of isolated serum and urinary antibodies to a single antigen.

Purified antibodies to tetanus toxoid have been separated from serum γG-globulins and from low molecular weight fragments of urinary γ-globulins (Fu fragments). Isolated Fu antibodies have been shown to be of low molecular weight and appear to be bivalent; they agglutinate antigen-coated red cells, fix complement and contain an average of five disulphide bonds, one of which is more labile than the remaining four. The antibody activity of the molecule is destroyed by reduction of this labile disulphide bond. These results are discussed in the light of current concepts of antibody structure.