Electron spin echo envelope modulation spectroscopy supports the suggested coordination of two histidine ligands to the Rieske Fe-S centers of the cytochrome b6f complex of spinach and the cytochrome bc1 complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria.
Electron spin echo envelope modulation (ESEEM) experiments performed on the Rieske Fe-S clusters of the cytochrome b6f complex of spinach chloroplasts and of the cytochrome bc1 complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria show modulation components resulting from two distinct classes of 14N ligands. At the g = 1.92 region of the Rieske EPR spectrum of the cytochrome b6f complex, the measured hyperfine couplings for the two classes of coupled nitrogens are A1 = 4.6 MHz and A2 = 3.8 MHz. Similar couplings are observed for the Rieske centers in the three cytochrome bc1 complexes. These ESEEM results indicate a nitrogen coordination environment for these Rieske Fe-S centers that is similar to that of the Fe-S cluster of a bacterial dioxygenase enzyme with two coordinated histidine ligands [Gurbiel, R. J., Batie, C. J., Sivaraja, M., True, A. E., Fee, J. A., Hoffman, B. M., & Ballou, D. P. (1989) Biochemistry 28, 4861-4871]. The Rieske Fe-S cluster lacks modulation components from a weakly coupled peptide nitrogen observed in water-soluble spinach ferredoxin. Treatment with the quinone analogue inhibitor DBMIB causes a shift in the Rieske EPR spectrum to g = 1.95 with no alteration in the magnetic coupling to the two nitrogen atoms. However, the ESEEM pattern of the DBMIB-altered Rieske EPR signal shows evidence of an additional weakly coupled nitrogen similar to that observed in the spinach ferredoxin ESEEM patterns.
Britt
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Laboratory of Chemical Biodynamics, Lawrence Berkeley Laboratory, Berkeley, California 94720.
Sauer
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K
Klein
M P
MP
Knaff
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DB
Kriauciunas
A
A
Yu
C A
CA
Yu
L
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Malkin
R
R
D000818:Animals; D002417:Cattle; D002736:Chloroplasts / Q000378:metabolism; D003573:Cytochrome b Group / Q000378:metabolism*; D045346:Cytochrome b6f Complex; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D014450:Electron Transport Complex III / Q000378:metabolism*; D006639:Histidine; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008433:Mathematics; D008929:Mitochondria, Heart / Q000201:enzymology*; D010944:Plants / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000201:enzymology*; D012247:Rhodospirillum rubrum / Q000201:enzymology*
D003573:Cytochrome b Group; D007506:Iron-Sulfur Proteins; D008024:Ligands; C037989:Rieske iron-sulfur protein; D006639:Histidine; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III