Transport effects on surface-volume biological reactions

Many cellular reactions involve a reactant in solution binding to or dissoc iating from a reactant confined to a surface. This is true as well for a BI Acore(TM), an optical biosensor that is widely used to study the interactio n of biomolecules. In the flow cell of this instrument, one of the reactant s is immobilized on a flat sensor surface while the other reactant hows pas t the surface. Both diffusion and convection Flay important roles in bringi ng the reactants into contact. Usually BIAcore(TM) binding data are analyze d using well known expressions that are valid only in the reaction-limited case when the Damkohler number Da is small. Asymptotic and singular perturb ation techniques are used to analyze dissociation of the bound state when D a is small and O(1). Linear and nonlinear integral equations result from th e analysis explicit and asymptotic solutions are constructed for physically realizable cases. In addition, effective rate constants are derived that i llustrate the effects of transport on the measured rate constants. All thes e expressions provide a direct way to estimate the rate constants from BIAc ore(TM) binding data.