World Library  
Flag as Inappropriate
Email this Article

Binding constant

Article Id: WHEBN0006747488
Reproduction Date:

Title: Binding constant  
Author: World Heritage Encyclopedia
Language: English
Subject: Filter binding assay, Equilibrium chemistry, Chemical equilibria, Chemical stability, Manchester Centre for Integrative Systems Biology
Collection: Equilibrium Chemistry
Publisher: World Heritage Encyclopedia

Binding constant

The binding constant is a special case of the equilibrium constant K. It is associated with the binding and unbinding reaction of receptor (R) and ligand (L) molecules, which is formalized as:

{\rm R} + {\rm L}\rightleftharpoons {\rm RL}.

The reaction is characterized by the on-rate constant k_{\rm on} and the off-rate constant k_{\rm off}, which have units of 1/(concentration time) and 1/time, respectively. In equilibrium, the forward binding transition {\rm R} + {\rm L} \to {\rm RL} should be balanced by the backward unbinding transition {\rm RL} \to {\rm R} + {\rm L}. That is,

k_{\rm on}\,\, = k_{\rm off}\,,

where , and represent the concentration of unbound free receptors, the concentration of unbound free ligand and the concentration of receptor-ligand complexes. The binding constant, or the association constant K_{\rm a} is defined by

K_{\rm a} = {k_{\rm on} \over k_{\rm off}} = \over \,}}.

An often considered quantity is the dissociation constant K_{\rm d} \equiv 1/K_{\rm a}, which has the unit of concentration, despite the fact that strictly speaking, all association constants are unitless values. The inclusion of units arises from the simplification that such constants are calculated solely from concentrations, which is not the case. Once chemical activity is factored into the correct form of the equation, a dimensionless value is obtained. For the binding of receptor and ligand molecules in solution, the molar Gibbs free energy \Delta G, or the binding affinity is related to the dissociation constant K_{\rm d} via

\Delta G = R T\ln},

in which R is the ideal gas constant, T temperature and the standard reference concentration c^{\ominus} = 1 mol / L.

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.