Inhibits signal transduction by increasing the GTPase activity of G protein alpha subunits thereby driving them into their inactive GDP-bound form. Binds selectively to G(z)-alpha and G(alpha)-i2 subunits, accelerates their GTPase activity and regulates their signaling activities. The G(z)-alpha activity is inhibited by the phosphorylation and palmitoylation of the G-protein. Negatively regulates mu-opioid receptor-mediated activation of the G-proteins. Forms a complex with G(alpha)z/i2 subunits and mu-opioid receptors; the formation of this complex results in mu-opioid receptor desensitization. Interacts with OPRM1 (By similarity). Shuttles between the cytoplasm/cell membrane and the nucleus Anchored to the membrane through palmitoylation. Fatty acylated. Heavily palmitoylated in the cysteine string motif (By similarity). N- and O-glycosylated in synapsomal membranes. Serine phosphorylated in synapsomal membranes. Sumoylated with SUMO1, SUMO2 and SUMO3. Sumoylation increases binding to the G-proteins, G(alpha)-i2 and G(z), and interaction with mu-opioid receptors.