Homologous receptors

Recombinant DNA technology has also facilitated detailed study of cytokine receptors. Based upon amino acid sequence homology, receptors are usually classified as belonging to one of six known superfamilies (Table 8.3). Individual members of any one superfamily characteristically display 20-50 per cent homology. Conserved amino acids normally occur in discrete bands or clusters, which usually correspond to a discrete domain in the receptor. Most receptors exhibit multiple domains. In some cases a single receptor may contain domains characteristic of two or more superfamilies. For example, the IL-6 receptor contains domains characteristic of both the haematopoietic and immunoglobulin superfamilies, making it a member of both. 

The opioid peptides can be viewed to contain two elements an essential message component that is recognized by a homologous receptor subsite... 

Another, homologous receptor that has more recently been characterized is sensitive to glycine only yet shares the conductivity for cations, so that glycine turns out not to be a purely inhibitory transmitter after all. 

Highly homologous receptor subtypes (ml, m2, m3 more than 95 % similarity) interact in a different way with the same Ugand. 

The phospholipase Cf enzymes are subject to a variety of regulatory influences. Phosphorylation by cAMP-dependent protein kinases ( protein kinase A) and by protein kinase C link the /f-isoforms to heterologous and homologous receptor pathways. 

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