alpha Subunit, G-Protein
The GTPase-containing subunits of Heterotrimeric GTP-Binding Proteins. When dissociated from the heterotrimeric complex these subunits interact with a variety of Second Messenger Systems. Hydrolysis of GTP by the inherent GTPase activity of the subunit causes it to revert to its inactive (heterotrimeric) form. The GTP-Binding Protein alpha subunits are grouped into Families according to the type of action they have on Second Messenger Systems.