Multiple conformations at functional site of hemerythrin: Evidence from resonance Raman spectra.

Resonance Raman spectra were obtained for monomeric oxymyohemerythrin and for the azide, thiocyanate, cyanate, cyanide, and fluoride adducts of metmyohemerythrin. The internal ligand vibrations in these complexes appear at essentially the same frequencies as those in the corresponding complexes of octameric hemerythrin. Likewise the Fe-O frequencies in H(2) (16)O do not depend on quaternary structure of the protein. The anionic adducts fall into two classes in regard to isotope exchange behavior in H(2) (18)O. They also manifest a novel photochemical transformation from one class of exchange behavior to the other. It seems evident that the functional site in hemerythrin exists in at least two different conformational states and that irradiation can stimulate isotope exchange in the exchange-resistant form.