[G proteins: GTP binding proteins in signal transduction].

A family of GTP-binding proteins (G proteins) couples receptors for hormones and neurotransmitters to diverse effectors in the cell. G proteins are membrane-bound GTPases composed of three distinct polypeptides. Cyclic AMP production, phosphoinositide breakdown, and ion channels are all known to be regulated via G proteins. Functional characterization, protein purification, labelling with bacterial toxins, specific antibodies and molecular cloning are tools which have helped to provide information on these proteins. Although the molecular properties of several G proteins are well known, the correct functional assignments are complex. Furthermore, we do not know how the various signal systems are involved in regulation of G protein activity.