Subunit interactions in pig heart fumarase--I. Study of tetramer-dimer equilibrium in dilute urea solutions.

1. Information about the interaction forces at the contact regions between fumarase subunits is obtained from kinetical and structural studies of dissociation and reassociation. 2. In dilute urea solutions an equilibrium between tetramers and dimers is established. 3. No appreciable unfolding of the individual subunits is observed in these conditions.