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intracellular membrane-associated proteins activated by several (for example, β-adrenergic) receptors; they serve as second messengers or transducers of the receptor-initiated response to intracellular elements such as enzymes to initiate an effect. These proteins have a high affinity for guanine nucleotides and hence are named G proteins.
Synonym(s): G-protein, GTP binding proteins, guanine nucleotide-binding protein, guanine-binding protein
Farlex Partner Medical Dictionary © Farlex 2012
G proteinsCell messengers that relay signals from over 1000 different cell membrane receptors to many different intracellular effectors such as enzymes and ion channels. G proteins have three subunits, alpha, beta, and gamma, each coded for by a different gene, selected from a total of 34 genes. G protein function is switched on and off by the binding and hydrolysis of guanosine triphosphate to the alpha subunit which is loosely attached to the others. Binding causes the beta and gamma fragments to separate as a dimer and to activate downstream effectors.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005