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. Expressed in brain and heart. Expressed in brain at protein level. Expressed in prefontal and visual cortex. Isoform 4 and isoform 5 are expressed ubiquitously. Isoform 1, isoform 2 and isoform 3 are not expressed in the cerebellum. 5 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.