Heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) dissociate into guanosine triphosphate (GTP)-bound alpha subunits and a complex of beta and gamma subunits after interaction with receptors. The GTP-alpha subunit complex activates appropriate effectors, such as adenylyl cyclase, retinal phosphodiesterase, phospholipase C, and ion channels. G protein beta gamma subunits have been found to have regulatory effects on certain types of adenylyl cyclase. In the presence of Gs alpha, the alpha subunit of the G protein that activates adenylyl cyclase, one form of adenylyl cyclase was inhibited by beta gamma, some forms were activated by beta gamma, and some forms were not affected by beta gamma. These interactions suggest mechanisms for communication between distinct signal-transducing pathways.