Inhibits signal transduction by increasing the GTPase activity of G protein alpha subunits thereby driving them into their inactive GDP-bound form. Activity on G(z)-alpha is inhibited by phosphorylation of the G-protein. Activity on G(z)-alpha and G(i)-alpha-1 is inhibited by palmitoylation of the G-protein (By similarity). Palmitoylated on Cys-2 and/or Cys-12. Phosphorylated by cyclic GMP-dependent protein kinase.