Bioactive substrate binding

Figure 5. Step 2b in the modified MacFarland bioactivity model. Binding, involving the change from a weak to a strong complex. Conformational changes in both substrate and receptor site may take place.

The quantity Aimf on which both transport and receptor binding of a bioactive substrate depend is variable in composition. It depends on the nature of the atoms or groups of atoms which make up the membrane surface or alternatively the receptor surface. 

So far, SAR studies for P-gp have been performed on the basis of classical QSAR principles which were designed for transporters or receptors, which naturally bind one specific substrate from an aqueous environment. The assumptions made are that (i) the modeled conformation is the bioactive one (ii) the binding site and/or mode is the same for all modeled compounds (iii) interactions between the drug and the binding site are mainly due to enthalpic processes (e.g., van der Waals interactions) and (iv) solvent or membrane effects are negligible (cf. Ref. [35]). 

A rare but serious event that can result from irreversible CYP inhibition is the development of a hypersensitivity reaction. The bioactivation of a drug and the formation of a covalent adduct between the activated substrate and the enzyme can lead to hapten formation and eventually to an idiosyncratic autoimmune response (usually in the form of autoimmune hepatitis) [14]. The hapten formation is the first key step toward the autoimmune response. The CYP macromolecule is made immunogenic ( foreign ) by the covalent binding of the electrophilic metabolites, and the immune reaction follows with the production of autoantibodies against the target molecule (not necessarily alkylated). 

The surface and type of selected immobilization method will affect the bioactivity, the concentration, and the target-binding ability of bound probe molecules. Gold and glass substrates are good candidates for the immobilization of biomolecules. These substrates have a number of favorable characteristics (1) they are chemically homogeneous and stable, (2) surface properties like wettability can be fine-tuned,... 

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