Acceleration of molecular complex dissociation by occlusion of rapid rebinding

Molecular complexes in biology are held together by non-covalent interactions. Explicit consideration of molecular diffusion suggests that the dissociation kinetics of these systems are not adequately explained by simple distinctions between ``bound'' and ``free'' states of its molecular components. We formulated physical models that describe the effect of competitor molecules on the dissociation of a complex. The models show that competitor acceleration of complex dissociation by occluding rapid re-association is a natural feature of a molecular competition that could play a significant role in a wide variety of biological regulatory processes. We use single-molecule fluorescence colocalization experiments on a model complex to test this prediction and show that the effect is observed in biologically relevant ranges of competitor concentration. The results also demonstrate that single-molecule colocalization experiments can accurately measure dissociation rates despite their limited spatiotemporal resolution.