Diffusion control of the binding of carcinoembryonic antigen ( CEA) with insoluble anti- CEA antibody.
Analysis of the kinetics of CEA binding to rabbit anti- CEA antibody insolubilized on filter paper discs provided six lines of evidence indicating diffusion control of this reaction: 1) The observed forward rate constant, k1obs, decreased when solvent viscosity was increased with sucrose or Ficoll. 2) k1obs per receptor site increased from 1.2 x 10(4) M-1 sec-1 to 2.6 x 10(4) M-1 sec-1 as receptor site density on immunosorbent discs decreased from 5.2 x 10(-13) to 2.1 x 10(-13) moles/disc. 3) Stirring the reacting mixture of CEA and insoluble anti- CEA increased k1obs from 1.2 x 10(4) M-1 sec-1 to 3.4 x 10(4) M-1 sec-1. 4) The activation energy for CEA-insoluble anti- CEA binding was indistinguishable (p greater than 0.1 by t-test) from 4.1 Kcal/mole expected for diffusion controlled reactions. 5) Bimolecular reaction theory predicted a diffusion limited forward rate constant, k1max, for CEA binding to insoluble anti- CEA, which was consistent with our observed k1 of 1.2 x 10(4) M-1 sec-1. 6) k1obs for CEA binding to soluble rabbit anti- CEA antibody was 6.4 x 10(4) M-1 sec-1, 5 times faster than the k1obs of the heterogeneous phase reaction for receptor site density of 5.2 x 10(-13) moles/disc. Diffusion control of ligand binding to insoluble receptors, as exemplified by the CEA-insoluble anti- CEA model system, may be a very general biologic phenomenon.[1]References
- Diffusion control of the binding of carcinoembryonic antigen (CEA) with insoluble anti-CEA antibody. Frackelton, A.R., Weltman, J.K. J. Immunol. (1980) [Pubmed]
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