Interaction of purified precipitating and non-precipitating (coprecipitating) antibodies with hapten and with haptenated protein. Evidence of an asymmetric antibody molecule.
The interaction of monovalent hapten dinitrophenyl epsilon-amino caproic acid (DNP-EACA) with purified IgG1 sheep anti-DNP precipitating and non-precipitating antibodies, and their F(ab')2, F(ab') and Fab fragments, was studied by fluorescence quenching and by a radioimmunoassay. The Scatchard plots of whole non-precipitating antibody and its F(ab')2 fragment showed a bi-modal curve that could be interpreted as due to the existence of two populations of sites with very different affinity for the ligand, each population representing 50% of the total number of sites. The F(ab) fragments of the non-precipitating antibody could be fractionated by immunoadsorption into two populations of high and low affinity whose association constants differed by more than 2 logs. The study of the interaction of whole antibodies with DNP-bovine serum albumin (BSA) demonstrated that each molecule of precipitating antibody can combine with two molecules of antigen but non-precipitating antibody cannot combine with more than one molecule of antigen. It is concluded that the molecule of non-precipitating antibody is asymmetric and has a site of high affinity and another of low affinity. As a consequence of this structure the non-precipitating antibody behaves functionally as univalent and is unable to form precipitates with the multivalent antigen and to activate effector mechanisms.
D000614:Aminocaproates / Q000276:immunology / Q000378:metabolism*; D000818:Animals; D000937:Antigen-Antibody Reactions; D000941:Antigens / Q000276:immunology; D001666:Binding Sites, Antibody; D011232:Chemical Precipitation; D004140:Dinitrophenols / Q000276:immunology; D006241:Haptens / Q000276:immunology*; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007074:Immunoglobulin G / Q000378:metabolism*; D007700:Kinetics; D012710:Serum Albumin, Bovine / Q000276:immunology / Q000378:metabolism*; D012756:Sheep
D000614:Aminocaproates; D000941:Antigens; D004140:Dinitrophenols; D006241:Haptens; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; C034638:dinitrophenyl-bovine serum albumin; C031746:6-N-(2,4-dinitrophenyl)aminohexanoic acid; D012710:Serum Albumin, Bovine