Stoichiometric characteristics and resonance Raman spectra of azidosemimethemerythrin.

With extra precautions to remove dissolved oxygen, reduction of aquomethemerythrin with dithionite occurs with a stoichiometry very close to 1.0. The aquosemimethemerythrin so produced combines with N3- ion almost on a 1:1 basis per monomer. Resonance Raman spectra of azidosemimethemerythrin differ from those of azidomethemerythrin in the position of the Fe-N stretching frequency and in the absence of a feature corresponding to a mu-oxo bridge, but in both complexes the internal azide stretch occurs at the same frequency and the substitution of isotopically unsymmetrical 15N14N-2 leads to a splitting of the Fe-N band. These observations provide some insight into the structural features of the binuclear functional site.

Raman and infrared spectroscopy of the oxo-bridged iron(III) complex, [Cl3Fe-O-FeCl3]-2 as a spectroscopic model for the oxo bridge in hemerythrin and ribonucleotide reductase.

Vibrational spectroscopic data were collected on the salt [C5H6N]2[Cl3FeOFeCl3] . C5H5N, which has previously been structurally characterized by X-ray crystallography. The modes associated with the oxo bridge were identified by experiments on the 18O-containing species. Spectra for the mu-16O complex contain Raman bands at 870, 458, and 203 cm-1 that shift to 826, 440, and 198 cm-1 in the mu-18O complex. These are respectively assigned to the asymmetric, symmetric, and angle deformations of the bent Fe-O-Fe moiety. A normal mode vibration analysis based on a simple valence force field for the Fe-O-Fe portion of the molecule provides surprisingly good agreement with these experimental frequencies and their assignments. The vibrational data for this simple inorganic complex confirm the assignment of a resonance Raman band around 500 cm-1 in the oxygen-carrying protein hemerythrin and enzyme ribonucleotide reductase as the symmetric stretch of an oxo bridge between two iron(III) centers.

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.

Resonance Raman studies and structure of a sulfide complex of methemerythrin.

The complex of sulfide and methemerythrin has been characterized by resonance Raman spectroscopy. At pH 8.0 the complex contains two irons and one S2- at the active site. The resonance Raman spectrum of the sulfidomethemerythrin complex contains only one vibration, at 444 cm-1. This vibration is assigned to an iron-sulfide stretch. The possibility that sulfidomethemerythrin contains a mu-sulfido bridge. FeIII-S2-FeIII, analogous to the proposed mu-oxo bridge in azidomethemerythrin is discussed.