Guanosine 5prime-[beta gamma-imido]triphosphate (GMP-PNP Gpp(NH)p) is a non-hydrolyzable analog of GTP that binds and irreversibly activates G proteins. Gpp(NH)p is used in a variety of applications that involve GTP binding including GTP-activation GTP-inhibition GTP transport GTP hydrolysis and GTP structure stabilization. Since a cycle of GTP binding hydrolysis and release is required for the initiation of protein translocation across the endoplasmic reticulum guanosine 5prime-[beta gamma-imido]triphosphate is often used in studies of protein synthesis. Gpp(NH)p is used to activate ADP-ribosylation factors and to modulate G proteins involved in cell signaling protein synthesis and other metabolic processes.