Bimodal sedimenting zones due to ligand-mediated interactions.

Ligand-mediated association-dissociation reactions can give rise to band sedimentation patterns showing bimodal bands despite instantaneous establishment of equilibrium. Weaker interactions result in unimodal bands whose sedimentation coefficients decrease with time of sedimentation and in characteristic patterns of total ligand. The implications of these results for fundamental investigations of protein interactions and for conventional analytical applications of zone sedimentation and molecular sieve chromatography are considered.