Competition in drug binding and horizontal ellipsis the race to equilibrium

Research output: Contribution to journalArticlepeer-review


Binding kinetics has become a popular topic in pharmacology due to its potential contribution to the selectivity and duration of drug action. Yet, the overall kinetic aspects of complex binding mechanisms are still merely described in terms of elaborate algebraic equations. Interestingly, it has been recommended some 10 years ago to examine such mechanisms in terms of binding fluxes instead of the conventional rate constants. Alike the velocity of product formation in enzymology, those fluxes refer to the velocity by which one target species converts into another one. Novel binding flux-based approaches are utilized to get a better visual insight into the “competition” between two drugs/ligands for a single target as well as between induced fit- and conformational selection pathways for a single ligand within a thermodynamic cycle. The present data were obtained by differential equation-based simulations. Early on, the ligand-binding steps “race” to equilibrium (i.e., when their forward and reverse fluxes are equal) at their individual pace. The overall/global equilibrium is only reached later on. For the competition association assays, this parting might produce a transient “overshoot” of one of the bound target species. A similar overshoot may also show up within a thermodynamic cycle and, at first glance, suggest that the induced fit pathway dominates. Yet, present findings show that under certain circumstances, it could rather be the other way round. Novel binding flux-based approaches offer visually attractive insights into crucial aspects of “complex” binding mechanisms under non-equilibrium conditions.

Original languageEnglish
Pages (from-to)147-157
Number of pages11
JournalFundamental and Clinical Pharmacology
Issue number1
Early online date18 Aug 2022
Publication statusPublished - Feb 2023

Bibliographical note

Funding Information:
We are very much indebted to Dr. David Swinney for helpful comments.

Publisher Copyright:
© 2022 Société Française de Pharmacologie et de Thérapeutique. Published by John Wiley & Sons Ltd.

Copyright 2023 Elsevier B.V., All rights reserved.


  • binding fluxes
  • competition binding
  • conformational selection
  • equilibrium binding
  • induced fit
  • kinetics


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