Authors: F Piazza P De Los Rios D Fanelli L Bongini U Skoglund
Publish Date: 2005/04/01
Volume: 34, Issue: 7, Pages: 899-911
Abstract
The encounter between anisotropic agents in diffusioncontrolled reactions is a topic of very general relevance in chemistry and biology Here we introduce a simplified model of encounter of an isotropic molecule with a pair of partially reacting agents and apply it to the encounter reaction between an antibody and its antigen We reduce the problem to the solution of dual series relations which can be solved iteratively yielding the exact solution for the encounter rate constant at any desired order of accuracy We quantify the encounter effectiveness by means of a simple indicator and show that the two binding centers systematically behave in an anticooperative fashion However we demonstrate that a reduction of the binding active sites allows the composite molecule to recover binding effectiveness in spite of the overall reduction of the rate constant In addition we provide a simple formula that enables one to calculate the anticooperativity as a function of the size of the binding site for any values of the separation between the two active lobes and of the antigen size Finally some biological implications of our results are discussed
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