The process of vision is initiated when the G protein-coupled receptor, rhodopsin (Rho),
absorbs a photon and transitions to its activated Rho∗ form. Rho∗ binds the heterotrimeric
G protein, transducin (Gt) inducing GDP to GTP exchange and Gt dissociation. Using
nucleotide depletion and affinity chromatography, we trapped and purified the resulting
nucleotide-free Rho∗· Gt complex. Quantitative SDS–PAGE suggested a 2: 1 molar ratio of
Rho∗ to Gt in the complex and its mass determined by scanning transmission electron …