Figure 7. Association and dissociation of heterotrimeric G protein and the effect of GDP on dissociation.
(a) Utilizing a global fit analysis the affinity (Kd) of G protein for μ-receptor was determined as 13 ± 1 nM for the BU72-bound receptor and 2.9 ± 0.8 nM for the morphine-bound receptor, though these are pseudo-affinity constants as the G protein binding was nearly irreversible on the time-scale studied. Only in the presence of nucleotide (b) did the BU72-bound heterotrimer rapidly dissociate.