The increase in Bmax suggests that a shift of the binding equilibrium occurs toward a stable ligand bound state for GluN2A, with a slower ligand dissociation rate.
The slow approach toward binding equilibrium may explain, in part, the slow kinetics of PHO5 induction and promoter nucleosome loss [27].
Contrarily, in the population-shift model, the enzyme is thought to adopt a conformational equilibrium among many native states, and substrates are able to selectively bind to a suitable native conformation, shifting the equilibrium toward the binding conformation.
The latter believes that the proteins or enzymes exist in the multiple conformations in the vicinity of its native state, and the ligand selectively binds to an active conformation to shift the equilibrium toward the binding conformation [ 68, 69].
An even slower approach toward binding equilibrium was previously observed by ChIP [28].
The spectra in solution are reproduced from López et al., where it was shown that each spectrum consists of two components, i and m, arising from distinct protein conformations, and that the effect of ligand binding was to shift the conformational equilibrium toward the m component.
In vitro, μ2Thr156 phosphorylation enhances the binding of AP2 to endocytic motifs (Höning et al., 2005; Olusanya et al., 2001; Ricotta et al., 2002) presumably by driving the equilibrium toward the cargo-binding-competent open form.
Addition of thrombin shifted the equilibrium toward the quadruplex (thrombin-binding conformation) that destroyed the hairpin structure and caused a change in the distance between the fluorophore and the quencher, resulting in a dequenching effect (Fig. 5a).
Binding of lauric acid clearly shifts the iron equilibrium toward the high-spin form.
Similarly, using the FRET methodology, an observed very rapid FRET decrease phase was interpreted to represent this shift in equilibrium toward the post-translocation state induced by nucleotide binding.
