FREE ENERGY OF SUBUNIT INTERACTIONS . HEMERYTHRIN

The association-dissociation equilibrium of hemerythrin has been studied by equilibrium ultracentrifugation. Dilution of the protein leads to extensive dissociation of the octamer at concentrations below about 0.04%. The equilibrium concentration distribution indicates that only monomers are present in equilibrium with octamers; and the association constant for 8Hr = Hr8 is 3.4 × 1036 m-7 for the azide complex of hemerythrin at 5°. This corresponds to a standard free-energy change of 6 kcal/mole for formation of 1 mole of monomer from octamer. An examination of freeenergy changes associated with small perturbations in structure of hemerythrin, or other proteins, indicates that these could have pronounced effects on the conformation of the macromolecule. © 1969, American Chemical Society. All rights reserved.