Homotropic cooperative binding of the first component of guinea pig complement to rabbit IgG-erythrocyte complexes: a possible allosteric effect.
Binding of the activated first component of guinea pig complement to immune complexes formed between dinitrophenylated erythrocytes and rabbit IgG antibody to 2,4-dinitrophenylhapten has been studied quantitatively. Cooperative binding was observed; it in volves no interactions between the domains on the erythrocyte surface that bind the activated first component of complement, or between the activated complement molecules in solution. By curve-fitting methods, we find that the data are consistent with an allosteric model, which assumes 10 binding sites per domain, a low allosteric equilibrium constant, and virtually exclusive binding to one of the isomers.
D000818:Animals; D000936:Antigen-Antibody Complex; D000937:Antigen-Antibody Reactions; D001665:Binding Sites; D002417:Cattle; D003165:Complement System Proteins / Q000378:metabolism*; D004140:Dinitrophenols; D004912:Erythrocytes / Q000276:immunology* / Q000378:metabolism; D005163:Factor Analysis, Statistical; D006168:Guinea Pigs; D006241:Haptens / Q000378:metabolism; D007106:Immune Sera; D007074:Immunoglobulin G / Q000378:metabolism; D007136:Immunoglobulins / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D012710:Serum Albumin, Bovine; D012756:Sheep; D013045:Species Specificity
D000936:Antigen-Antibody Complex; D004140:Dinitrophenols; D006241:Haptens; D007106:Immune Sera; D007074:Immunoglobulin G; D007136:Immunoglobulins; D012710:Serum Albumin, Bovine; D003165:Complement System Proteins