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G Bunker

Publications and source records attributed to G Bunker.

24 records · Page 2Linked to original sources
PubMed1987

Extended X-ray absorption fine structure studies on the iron-containing subunit of ribonucleotide reductase from Escherichia coli.

Iron K-edge X-ray absorption spectra were obtained on the protein B2, the small subunit of ribonucleotide reductase from Escherichia coli. Protein B2 contains a binuclear iron center with many properties in common with the iron center of oxidized hemerythrins. The extended X-ray absorption fine structure (EXAFS) measurements on protein B2 were analyzed and compared with published data for oxyhemerythrin. In protein B2 there are, in the first coordination shell around each Fe atom, five or six oxygen or nitrogen atoms that are directly coordinated ligands. In oxyhemerythrin there are six ligands to each iron. As in oxyhemerythrin, one of the ligands in the first shell of protein B2 is at a short distance, about 1.78 A, confirming the existence of a mu-oxo bridge. The other atoms of the first shell are at an average distance of 2.04 A, which is about 0.1 A shorter than in oxyhemerythrin. In protein B2 the Fe-Fe distance is in the range 3.26-3.48 A, and the bridging angle falls between 130 and 150 degrees. On the basis of these data, there is no direct evidence for any histidine ligands in protein B2, but the noise level leaves way for the possibility of a maximum of about three histidines for each Fe pair. The X-ray absorption spectrum of a hydroxyurea-treated sample was not significantly different from that of the native protein B2, which implies that no significant alteration in the structure of the iron site occurs upon destruction of the tyrosine radical.

Escherichia coli↗
PubMed1986

Extended X-ray absorption fine structure studies of Zn2Fe2 hybrid hemoglobins: absence of heme bond length changes in half-ligated species.

Metal hybrid hemoglobins, in which Zn(II) replaces Fe(II), have been structurally characterized by extended X-ray absorption structure (EXAFS) studies. Since Zn and Fe have very different K absorption edge energies, the structures of the ligated (Fe) and unligated (Zn) sites could be examined independently within a single molecule that mimics an intermediate ligation state. The observed EXAFS spectra and associated structural parameters are compared among the ligand free (alpha Zn)2(beta Zn)2, half-ligated (alpha FeCO)2(beta Zn)2 and (alpha Zn)2(beta FeCO)2, and fully ligated (alpha FeCO)2(beta FeCO)2 systems.

Heme↗
PubMed1982

An x-ray absorption study of the iron site in bacterial photosynthetic reaction centers.

Measurements were made of the extended x-ray absorption fine structure (EXAFS) of the iron site in photosynthetic reaction centers from the bacterium Rhodopseudomonas sphaeroides. Forms with two quinones, two quinones with added o-phenanthroline, and one quinone were studied. Only the two forms containing two quinones maintained their integrity and were analyzed. The spectra show directly that the added o-phenanthroline does not chelate the iron atom. Further analysis indicates that the iron is octahedrally coordinated by nitrogen and/or oxygen atoms located at various distances, with the average value of about 2.14 A. The analysis suggests that most of the ligands are nitrogens and that three of the nitrogen ligands belong to histidine rings. This interpretation accounts for several unusual features of the EXAFS spectrum. We speculate that the quinones are bound to the histidine rings in some manner. Qualitative features of the absorption edge spectra also are discussed and are related to the Fe-ligand distance.

Iron↗