Abstract
A complex of rabbit IgG antibody with horseradish peroxidase covalently linked to Sepharose 4B was used as an insoluble immune complex for studying the binding of complement factor Clq, protein A from Staphylococcus aureus, and its IgG-binding fragments AB and B, to rabbit IgG. It was shown that protein A (mol. wt approx. 42,000) and fragments AB and B (mol. wts approx. 14,000 and 7000, respectively) inhibited the binding of Clq to insoluble immune complex at 4°C. However, at 37°C fragment B did not inhibit this binding. On the other hand, Clq, when bound to an insoluble immune complex, almost completely blocked the binding of protein A and fragment B at both temps. The higher affinity of Clq for its C H2-binding site than of fragment B for its C H2-binding site may explain the displacement of the latter from the C H2 domain. The mutual inhibition of the binding of Clq and protein A (and its smaller fragments) indicates that the binding sites for Clq and protein A are closely located in the C H2 domain.
Published Version
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