Effect of ethoxyformic anhydride on the Rieske iron-sulfur protein of bovine heart ubiquinol: Cytochromecoxidoreductase (original) (raw)
Related papers
Biochemistry, 1991
Electron spin echo envelope modulation (ESEEM) experiments performed on the Rieske Fe-S clusters of the cytochrome b$complex of spinach chloroplasts and of the cytochrome bcl complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria show modulation components resulting from two distinct classes of I4N ligands. At the g = 1.92 region of the Rieske EPR spectrum of the cytochrome b$complex, the measured hyperfine couplings for the two classes of coupled nitrogens are A I = 4.6 M H z and A2 = 3.8 MHz. Similar couplings are observed for the Rieske centers in thc three cytochrome bc, 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 Biochemistry 28, 4861-48711. The Rieske Fe-S cluster lacks modulation components from a weakly coupled peptide nitrogen observed in water-soluble spinach ferredoxin. Trcatment with the quinone analogue inhibitor DBMIB causes a shift in the Rieske EPR spectrum to g = 1.95 with no alteration in the magnetic couplings 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 ferrodoxin ESEEM patterns.
Biophysical Journal, 2008
The alternative low-spin states of Fe 31 and Fe 21 cytochrome c induced by SDS or AOT/hexane reverse micelles exhibited the heme group in a less rhombic symmetry and were characterized by electron paramagnetic resonance, UV-visible, CD, magnetic CD, fluorescence, and Raman resonance. Consistent with the replacement of Met 80 by another strong field ligand at the sixth heme iron coordination position, Fe 31 ALSScytc exhibited 1-nm Soret band blue shift and e enhancement accompanied by disappearance of the 695-nm charge transfer band. The Raman resonance, CD, and magnetic CD spectra of Fe 31 and Fe 21 ALSScytc exhibited significant changes suggestive of alterations in the heme iron microenvironment and conformation and should not be assigned to unfold because the Trp 59 fluorescence remained quenched by the neighboring heme group. ALSScytc was obtained with His 33 and His 26 carboxyethoxylated horse cytochrome c and with tuna cytochrome c (His 33 replaced by Asn) pointing out Lys 79 as the probable heme iron ligand. Fe 31 ALSScytc retained the capacity to cleave tertbutylhydroperoxide and to be reduced by dithiothreitol and diphenylacetaldehyde but not by ascorbate. Compatible with a more open heme crevice, ALSScytc exhibited a redox potential ;200 mV lower than the wild-type protein (1220 mV) and was more susceptible to the attack of free radicals.
Proceedings of the National Academy of Sciences, 1998
We have analyzed crystal structures of cytochrome bc 1 complexes with electron transfer inhibitors bound to the ubiquinone binding pockets Q i and/or Q o in the cytochrome b subunit. The presence or absence of the Q i inhibitor antimycin A did not affect the binding of the Q o inhibitors. Different subtypes of Q o inhibitors had dramatically different effects on the mobility of the extramembrane domain of the iron–sulfur protein (ISP): Binding of 5-undecyl-6-hydroxy-4,7-dioxobenzothiazol and stigmatellin (subtype Q o –II and Q o –III, respectively) led to a fixation of the ISP domain on the surface of cytochrome b , whereas binding of myxothiazol and methoxyacrylate-stilbene (subtype Q o –I) favored release of this domain. The native structure has an empty Q o pocket and is intermediate between these extremes. On the basis of these observations we propose a model of quinone oxidation in the bc 1 complex, which incorporates fixed and loose states of the ISP as features important for ...
Role of protonatable groups of bovine heart bc1 complex in ubiquinol binding and oxidation
European Journal of Biochemistry, 2001
The pH dependence of the initial reaction rate catalyzed by the isolated bovine heart ubiquinol-cytochrome c reductase (bc 1 complex) varying decylbenzoquinol (DBH) and decylbenzoquinone (DB) concentrations was determined. The affinity for DBH was increased threefold by the protonation of a group with pK a ¼ 5.7^0.2, while the inhibition constant (K i ) for DB decreased 22 and 2.8 times when groups with pK a ¼ 5.2^0.6 and 7.7^0.2, respectively, were protonated. This suggests stabilization of the protonated form of the acidic group by DBH binding. Initial rates were best fitted to a kinetic model involving three protonatable groups. The protonation of the pK a < 5.7 group blocked catalysis, indicating its role in proton transfer. The kinetic model assumed that the deprotonation of two groups (pK a values of 7.5^0.03 and < 9.2) decreases the catalytic rate by diminishing the redox potential of the ironsulfur (Fe-S) cluster. The protonation of the pK a < 7.5 group also decreased the reaction rate by 80 -86%, suggesting its role as acceptor of a proton from ubiquinol. The lack of effect on the K m for DBH when the pK a 7.5-7.7 group is deprotonated suggests that hydrogen bonding to this residue is not the main factor that determines substrate binding to the Q o site. The possible relationship of the pK a 5.2 -5.7 and pK a 7.5 -7.7 groups with Glu272 of cytochrome b and His161 of the Fe -S protein is discussed.
Biochemical Journal, 1987
We have studied the cd spectra of the'Rieske'iron-sulphur protein isolated from the ubiquinol: cytochrome c reductase (bc1 complex) of bovine heart mitochondria. Both the oxidized and the reduced form of the'Rieske'protein display a series of well-resolved cd features resembling those reported for the'Rieske'-type iron-sulphur protein purified from the bacterium Thermus thermophilus [Fee, Findling, Yoshida, Hille, Tarr, Hearshen, Dunham, Day, Kent & Münck (1984) J. Biol, Chem. 259, 124-133]. In particular, the difference ...
European Journal of Biochemistry, 1987
The effect of the histidine-modifier ethoxyformic anhydride (EFA) on the enzymatic properties of the mitochondrial zyxwvutsrq b-el complex (ubiquinolcytochrome c reductase) has been investigated. Chemical modification by EFA inhibited to the same extent the reductase and the proton translocating activity of the complex. In particular EFA modification of the complex resulted in: (a) strong inhibition of the antimycin-insensitive reduction of b cytochromes; (b) inhibition of the antimycin-promoted oxidant-induced reduction of b cytochromes and (c) inhibition of oxidation of pre-reduced b cytochromes.