Functional Biochemistry of Toxicant Receptors

Some ligands do not interact principally with cell surface receptors, but diffuse into cells and bind to intracellular receptors in the cytoplasm. For example, ligand binding to cytoplasmic steroid receptors initiates a process that is not well understood but that involves the movement of steroid-bound receptor into the cell nucleus, where the receptor molecule interacts with genomic material, resulting in alterations in gene expression and protein synthesis. 

As will become clear, this chapter is focused on toxicants for which the receptor is a high-affinity recognition site of the type discussed in the previous paragraphs. It should be noted explicitly that other toxicants have receptors, but fall into more complex situations not appropriate for this chapter. For example, some toxicants inhibit enzymes, or are themselves enzymes. Such interesting compounds include the organophosphate and carbamate insecticides (acetylcholine esterase inhibitors) and diphtheria toxin (an enzyme). 

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