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FIGURE 9.8 Elementary steps involved in the binding of trivalent antigen in solution to divalent antibody covalently attached to the surface.

is in solution and the antigen is covalently or noncovalently immobilized to the surface. The elementary steps involved in such a reaction are shown in Fig. 9.9. Once again, the nonspecific binding step is not shown but must be included before deriving a reaction rate expression. Figure 9.9a shows the elementary steps involved in the dual-step binding of divalent antibody in solution to monovalent antigen noncovalently or covalently attached to the surface. Figure 9.9b shows the elementary steps involved in the dual-step binding of divalent antibody in solution to trivalent antigen noncovalently or covalently attached to the surface.

Other suitable examples of antigen-antibody binding may also be possible. Be aware that all of the discussion presented in this chapter and in Chapter 8 should be applicable, with minor modifications if necessary, to analyte-receptor binding reactions in general.

PACs are one possible type of antigens that exhibit multivalencies and different binding sites for antibody binding. It is highly probable that as an antibody binds to an antigen-binding site, it either makes easier or constrains (owing to induced conformational changes on the molecule immobilized on

Bivalent antibody

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