Journal of Mathematical Chemistry

, Volume 51, Issue 2, pp 672–695 | Cite as

On the interaction of two different types of ligands binding to the same molecule part I: basics and the transfer of the decoupled sites representation to systems with n and one binding sites

  • Johannes W. R. Martini
  • Martin Schlather
  • G. Matthias Ullmann
Open Access
Original Paper

Abstract

The decoupled sites representation (DSR) for one type of ligand allows to regard complex overall titration curves as sum of classical Henderson-Hasselbalch (HH) titration curves. In this work we transfer this theoretical approach to molecules with different types of interacting ligands (e.g. protons and electrons), prove the existence of decoupled systems for n1 and one binding sites for two different ligands, and point out some difficulties and limits of this transfer. A major difference to the DSR for one type of ligand is the loss of uniqueness of the decoupled system. However, all decoupled systems share a unique set of microstate probabilities and each decoupled system corresponds to a certain permutation of these microstate probabilities. Moreover, we show that the titration curve of a certain binding site in the original system can be regarded as linear combination of the titration curves of the individual sites of the decoupled system if the weights of the linear combination are substituted by functions in the activity of the second ligand. In the underlying model with only pairwise interaction, an important observation of our theoretical investigation is the following: Even though the binding sites of ligand L1 may not interact directly, they can show secondary interaction due to the interaction with the second type of ligand. This means, if the activity of the second ligand is fixed and we regard the 1-dimensional titration curve of an individual binding site for ligand L1 depending on its activity, we may observe a strong deviation from the classical HH shape in spite of non-interacting sites for ligand L1.

Keywords

Decoupled sites representation Protonation Electron binding Different ligands Binding polynomial Interaction energy Binding energy Transport Transfer Photosynthesis Receptor 

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Copyright information

© The Author(s) 2012

Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.

Authors and Affiliations

  • Johannes W. R. Martini
    • 1
  • Martin Schlather
    • 2
  • G. Matthias Ullmann
    • 3
  1. 1.Institut für Mathematische StochastikGeorg-August Universität GöttingenGöttingenGermany
  2. 2.Institut für MathematikUniversität MannheimMannheimGermany
  3. 3.Bioinformatik/StrukturbiologieUniversität BayreuthBayreuthGermany

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