STRUCTURAL WATER IN OXIDIZED AND REDUCED HORSE HEART CYTOCHROME-C

The existence of structural water in the interior of both oxidized and reduced horse-heart cytochrome c in solution is demonstrated using nu clear magnetic resonance spectroscopy. Six water molecules have been l ocated in ferrocytochrome c and five in ferricytochrome c, with reside nce times greater than a few hundred picoseconds. Two water molecules are located in the haem crevice, one of which is found to undergo a la rge change in position with a change of oxidation state. Both of these observations indicate that buried structural waters in the haem crevi ce have, by microscopic dielectric effects, significant roles in the s etting of the solvent reorganization energy associated with electron t ransfer.