Competition in drug binding and … the race to equilibrium

Slow-binding inhibitors of enzymes: kinetic characteristics and pharmacological interest

Currently, the search for new slow-binding inhibitors of enzymes (SBI) and their identification primary in vitro studies still attracts much attention in the context of their potential role as putative pharmacological agents for the treatment of various diseases. In contrast to their classical reversible analogues, SBI exhibit a slow enzyme binding kinetics, where the equilibrium steady-state is reached not in microseconds, but after longer time intervals. Such compounds could be promising drugs, because regardless of their pharmacokinetics in the bloodstream, they have such advantages as high affinity for the target enzyme, long residence time on the target, and therefore, prolonged action. These pharmacological properties ensure optimized dosage of drugs required to achieve high activity with less side effects. In this review we have considered mechanisms of SBI interaction with enzyme targets, the principles of their recognition at the level of in vitro studies and analysis of binding and kinetic parameters.

The complexities of ligand/receptor interactions: Exploring the role of molecular vibrations and quantum tunnelling

Molecular vibrations and quantum tunneling may link ligand binding to the function of pharmacological receptors. The well-established lock-and-key model explains a ligand's binding and recognition by a receptor; however, a general mechanism by which receptors translate binding into activation, inactivation, or modulation remains elusive. The Vibration Theory of Olfaction was proposed in the 1930s to explain this subset of receptor-mediated phenomena by correlating odorant molecular vibrations to smell, but a mechanism was lacking. In the 1990s, inelastic electron tunneling was proposed as a plausible mechanism for translating molecular vibration to odorant physiology. More recently, studies of ligands' vibrational spectra and the use of deuterated ligand analogs have provided helpful information to study this admittedly controversial hypothesis in metabotropic receptors other than olfactory receptors. In the present work, based in part on published experiments from our laboratory using planarians as an experimental organism, I will present a rationale and possible experimental approach for extending this idea to ligand-gated ion channels.