ABSTRACT
X-ray absorption spectroscopy has been used to study the dimeric iron center in azidomethemerythrin from Phascolopsis gouldii. Absorption edge data confirm that the two iron atoms are present as Fe(III) and suggest a hexa-coordination site for each of the iron atoms. The extended x-ray absorption fine structure (EXAFS) analysis provides direct structural evidence of a mu-oxo bridge between the two iron atoms at an average Fe-O distance of 1.71-1.76 A. Analysis using a multiple-scattering formalism calculates upper limits of 165 degrees for the Fe-O-Fe bridging angle and 3.38 A for the Fe-Fe distance. This result agrees with current crystallographic models being determined by refinement of structures of two azidomethemerythrins.
Subject(s)
Hemerythrin , Invertebrates/analysis , Iron , Metalloproteins , Animals , Binding Sites , Ferric Compounds , Fourier Analysis , Hemerythrin/analogs & derivatives , Spectrophotometry, AtomicABSTRACT
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.
ABSTRACT
The complete amino acid sequence of muscle hemerythrin (myohemerythrin) from the sipunculid Themiste (syn. Dendrostomum) pyroides has been determined by analysis of tryptic, chymotryptic, and cyanogen bromide peptides. The primary structure of myohemerythrin differs substantially from that of coelomic hemerythrins of Phascolopsis (syn. Golfingia) gouldii and Themiste pyroides, the amino acid sequence of the muscle protein being only 46 and 45% homologous with the respective coelomic hemerythrins. The most extensive regions of homology between muscle and coelomic proteins occur near the terminii. These and other shorter regions of homology are interpreted in terms of the essential iron ligand residues of the active center.
Subject(s)
Hemerythrin , Metalloproteins , Muscle Proteins , Amino Acid Sequence , Amino Acids/analysis , Animals , Annelida , Chymotrypsin , Cyanogen Bromide , Peptide Fragments/analysis , TrypsinABSTRACT
X-ray diffraction studies have produced a low resolution image and also located the iron atoms of a monomeric hemerythrin from muscles of a sipunculan worm. These results reveal the course of the polypeptide chain and some details of the active center.
