DT diaphorase exists as a dimer-tetramer equilibrium in solution

The quaternary behaviour of DT diaphorase in solution has been investigated by hydrodynamics under a range of conditions. At neutral pH DT diaphorase is shown to exist as a tightly-associated homodimer in a dimer-tetramer equilibrium. Concentrations of the chaotropic agent potassium thiocyanate (KSCN) of greater than 200 mm result in irreversible loss of the FAD cofactor and denaturation of the homodimer though this agent appears to be ineffective in disrupting intermolecular association. These data conform to a model in which under extreme dissociation conditions, the folded dimer is in equilibrium with the unfolded monomer and are consistent with evidence from the X-ray structure and proposed catalytic mechanism where both monomers are catalytically interdependent. Received: 1 November 1996 / Accepted: 30 December 1996