Homotropic Cooperative Binding of the First Component of Guinea Pig Complement to Rabbit IgG-Erythrocyte Complexes: A Possible Allosteric Effect*
Abstract
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.
Footnotes
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↵ * Part of this work was presented to the Graduate College, Univ. of Iowa, in partial fulfillment of the requirements for the Ph.D. degree, August, 1970. Presented in preliminary form at the fourth International Complement Workship, Baltimore, Md., January, 1971.
