Other qualifications for a receptor High affinity:Most endogenous ligands bind to their cognate receptors with high affinities(usually in the range of nmol/L) Reversibility:In most cases,the bound ligand can be dissociated from the receptor,or replaced by another ligand that also bind to the same receptor Subtypes and subunits:Many receptors have subtypes, which are structurally and functionally similar receptors (but functions could be different).Some receptors are composed of multiple subunits Classification of receptors(by location) Cell surface receptors:Most receptors are present on cell surface,which is the boundary between intracellular environment and extracellular environment Cytoplasmic receptors:Usually participate in the transport of ligands and/or their signaling Nuclear receptors:Usually involved in transcriptional regulationOther qualifications for a receptor • High affinity: Most endogenous ligands bind to their cognate receptors with high affinities (usually in the range of nmol/L) • Reversibility: In most cases, the bound ligand can be dissociated from the receptor, or replaced by another ligand that also bind to the same receptor • Subtypes and subunits: Many receptors have subtypes, which are structurally and functionally similar receptors (but functions could be different). Some receptors are composed of multiple subunits • Cell surface receptors: Most receptors are present on cell surface, which is the boundary between intracellular environment and extracellular environment • Cytoplasmic receptors: Usually participate in the transport of ligands and/or their signaling • Nuclear receptors: Usually involved in transcriptional regulation Classification of receptors (by location)