G-protein beta-gamma complex Opsins that act as GEFs for G alpha-t Authored: Jassal, B, 2009-05-14 14:29:50 Edited: Jassal, B, 2009-05-14 14:29:50 Pubmed16634148 Pubmed2534964 Pubmed8406495 Reactome Database ID Release 43420883 Reactome, http://www.reactome.org ReactomeREACT_18400 Reviewed: D'Eustachio, P, 2009-05-29 07:44:22 Transducin (Gt) is a heterotrimeric G protein encoded by GNAT genes and is naturally expressed in vertebrate retina rods and cones. There are two types, alpha-1 chain (expressed in rods by GNAT1) (Lerea CL et al, 1989) and alpha-2 chain (expressed in cones by GNAT2) (Morris TA and Fong SL, 1993). Activation of the Gt alpha subunit results in the "vertebrate phototransduction cascade" (Chen CK, 2005). Cyclic GMP Phosphodiesterase is activated which lowers cGMP levels (an intracellular second messenger molecule). Lower cGMP levels can then lead to the closure of cGMP-regulated Na+ and Ca2+ ion channels and a hyperpolarized membrane potential.<br> G-alpha(t)-GTP G-alpha(t)-GDP:G-beta-gamma