Immunological localization of the GTP-binding protein Go in different tissues of vertebrates and invertebrates.

Bovine brain contains two GTP-binding proteins, Gi and Go, which are substrates for ADP ribosylation by pertussis toxin. The Gi protein mediates hormone and GTP inhibition of adenylate cyclase, but the function and the precise tissue distribution of Go are unknown. To immunologically probe the localization of Go, we have purified the Go alpha and G beta, gamma subunits of Go and have raised antibodies against them. The polyclonal anti-Go alpha antibodies obtained were very selective for Go alpha compared to Gi alpha or Gs alpha. The positive Go alpha and G beta, gamma immunoreactivities were investigated in different tissues of vertebrates and invertebrates on immunoblots after gel electrophoresis of the crude membranes. The anti-G beta, gamma antibodies recognized a 35-36-kDa protein in brain of vertebrates such as mammals (rat), avians (pigeon), amphibians (frog), fish (trout), and reptiles (turtle) but not in the invertebrates such as molluscs (snail) and insects (locust). With the anti-Go alpha antibodies a high level of immunoreactivity was detected at molecular weights of 39,000-40,000 in the brain of invertebrates as well as in the central nervous system of vertebrates. Moreover, ADP ribosylation with pertussis toxin occurred in the nervous system of invertebrates. These results suggest that the GTP-binding proteins of invertebrates either are devoid of G beta, gamma subunit or, more probably, possess immunologically different G beta, gamma subunits when compared to those of vertebrates. In the vertebrates, Go alpha immunoreactivity was also present in the peripheral nervous system in areas such as the superior cervical ganglia and sciatic nerve. When examined with the anti-Go alpha antibodies, the neuro-and adenohypophysis exhibited a similar immunoreactivity which was about 6 times lower than in brain. Our antibodies also recognized a 40-kDa protein in human adipocytes but at a concentration 17 times lower than that recognized in brain. Taken together, these data show that the Go alpha subunit is well conserved through evolution and, furthermore, confirm that Go alpha is not strictly limited to the nervous system. This suggests that the protein Go ensures a function required for neuronal activity but also present in some other non-nervous tissues.