The Nature of Receptors and Criteria for Receptor Identity

Lipoproteins or glycoproteins are the macromolecules that most commonly form receptors. They are often firmly embedded in the plasma membrane or cell-organelle membrane as intrinsic proteins (see section 7.1). At times, this renders their isolation and subsequent functional reconstitution difficult, as their structure may be dependent upon the surrounding membrane. Isolation of such a receptor molecule may cause its structural collapse, even to the extent that specific binding properties are lost. 

Pure proteins are frequent drug receptors, as in the case of enzymes. Many drugs exert their effects by specifically affecting enzymes involved in vital biochemical reactions (see section 8.2). 

Nucleic acids comprise an important category of drug receptors. A number of antibiotics and antirnmor agents either interfere directly with DNA replication or transcription, or inhibit translation of the genetic message at the ribosome level. Certain steroid hormones may also have DNA as their acceptor site (see chapter 8). 

When one starts to work with a new class of molecules or a new tissue, it is important to use an extensive set of criteria for receptor identification in both in vitro and in vivo smdies. These criteria are as follows  

The receptor should be present in the tissues in quantities commensurate with established receptor concentrations (10-100 pmol/g). 

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