ABSTRACT
Chapter 2 in Part I outlined ant-agonism and inhibition by intervention. To recapitulate, ‘intervention’ means mutually inclusive, i.e., two different ligands can bind simultaneously to their respective binding sites, while the two ligands do not bind at either site. There is no colateral binding possible (Section 2.6.3 and Fig. 2.4). On the other hand, when such a two-sited receptive unit for both interventor and agonist is also capable of a ‘twostate’-switch, R /X R*, its full thermodynamic reaction scheme involves eight receptor conformations, and ligand interaction at the secondary binding site is now denoted ‘modulation’ rather than ‘intervention’. This type of reaction scheme is covered in Chapter 7 by the allosteric two-state model (ATSM).
