Molecular Motion at Binding Equilibrium

1. Association & dissociation at binding equilibrium
(in a single compartment):
2. Association & dissociation at binding equilibrium
(in two compartments separated by a dialysis membrane):

What this animation is intended to illustrate:
1. In the upper panel:
The small molecules (ligands) and the macromolecules (protein) can both diffuse freely in solution. At this equilibrium, the protein is about half-saturated on average.
2. In the lower panel:
a) The ligands can diffuse freely between both cells of the dialysis chamber.
b) The macromolecules are too large to pass through the semipermeable dialysis membrane; thus, they are restricted to the left compartment.
c) At equilibrium, the concentration of free ligand is identical, on average, in both cells.
d) Complexes between the protein and ligand (ML) continue to dissociate and to rebind ligand at equilibrium. On average, the concentration of ML = 2 B/b, as shown in the calculation.

(Click the image to speed up the motion; click anywhere else to stop it.)
The Macromedia Director files (particlesNP.dcr & particlesNPS.dcr) were written by Tom Manderfield.