scholarly journals The circular-dichroic properties of the ‘Rieske’ iron-sulphur protein in the mitochondrial ubiquinol: cytochrome c reductase

1987 ◽  
Vol 241 (1) ◽  
pp. 285-290 ◽  
Author(s):  
M Degli Esposti ◽  
F Ballester ◽  
G Solaini ◽  
G Lenaz
Keyword(s):  
Cytochrome C ◽  
Thermus Thermophilus ◽  
Reduced Form ◽  
Bc1 Complex ◽  
Rieske Protein ◽  
Difference Spectra ◽  
Cytochrome C Reductase ◽  
Negative Band ◽  
The Difference ◽  
Circular Dichroic

We have studied the c.d. 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 c.d. 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 spectra, reduced minus oxidized, of both proteins have a distinctive negative band at 497 nm. The c.d. features characteristic of the isolated ‘Rieske’ protein were found in the dichroic spectra of the whole bc1 complex in the region between 450 and 520 nm. The reduction of the enzyme by ascorbate or ubiquinol is accompanied by the formation of a negative band at about 500 nm that corresponds, in all its c.d. properties, to the specific dichroic absorption of the reduced ‘Rieske’ iron-sulphur protein.

The cytochrome system in Mycobacterium lepraemurium

1974 ◽  
Vol 20 (7) ◽  
pp. 943-947 ◽  
Author(s):  
M. Ishaque ◽  
Laszlo Kato
Keyword(s):  
Cytochrome C ◽  
Respiratory Chain ◽  
Cell Suspensions ◽  
Reduced Form ◽  
Difference Spectra ◽  
Whole Cell ◽  
Chain System ◽  
Cytochrome O ◽  
The Difference ◽  
Mycobacterium Lepraemurium

The respiratory chain system of cell suspensions of Mycobacterium lepraemurium was investigated spectrophotometrically. The results obtained indicated that whole cell preparations contained flavins, cytochromes of the a + a3 and b type, as well as two CO-binding pigments; cytochromes a3–CO and a second pigment similar to cytochrome o. The cytochromes were found to be in the reduced form. The presence of cytochrome systems could only be shown after the cell suspensions in the reference cuvette were exposed to oxygen. The positions of the peaks in the difference spectra were similar when the cell suspensions were reduced anaerobically without added substrate or treated with dithionite. The whole cell suspensions of M. lepraemurium were not found to contain detectable quantities of cytochrome c.

scholarly journals The effect of complex-formation with polyanions on the redox properties of cytochrome c

1980 ◽  
Vol 192 (2) ◽  
pp. 687-693 ◽  
Author(s):  
L C Petersen ◽  
R P Cox
Keyword(s):  
Cytochrome C ◽  
Complex Formation ◽  
Reaction Rates ◽  
Reduced Form ◽  
Stable Complex ◽  
Phase System ◽  
Two Phase ◽  
The Difference ◽  
Low Ionic Strength ◽  
Positively Charged

1. The stable complex formed between mammalian cytochrome c and phosvitin at low ionic strength was studied by partition in an aqueous two-phase system. Oxidized cytochrome c binds to phosvitin with a higher affinity than reduced cytochrome c. The difference was equivalent to a decrease of the redox potential by 22 mV on binding. 2. Complex-formation with phosvitin strongly inhibited the reaction of cytochrome c with reagents that react as negatively charged species, such as ascorbate, dithionite, ferricyanide and tetrachlorobenzoquinol. Reaction with uncharged reagents such as NNN‘N’-tetramethylphenylenediamine and the reduced form of the N-methylphenazonium ion (present as the methylsulphate) was little affected by complex-formation, whereas oxidation of the reduced cytochrome by the positively charged tris-(phenanthroline)cobalt(III) ion was greatly stimulated. 3. A similar pattern of inhibition and stimulation of reaction rates was observed when phosvitin was replaced by other macromolecular polyanions such as dextran sulphate and heparin, indicating that the results were a general property of complex-formation with polyanions. A weaker but qualitatively similar effect was observed on addition of inositol hexaphosphate and ATP. 4. It is suggested that the effects of complex-formation with polyanions on the reactivity of cytochrome c with redox reagents are mainly the result of replacing the positive charge on the free cytochrome by a net negative charge. Any steric effects on polyanion binding are small in comparison with such electrostatic effects.

scholarly journals Mechanisms of Reaction of Some Flavoprotein Enzymes with Oxygen

1965 ◽  
Vol 49 (1) ◽  
pp. 201-211
Author(s):  
Quentin H. Gibson
Keyword(s):  
Amino Acid ◽  
Cytochrome C ◽  
Glucose Oxidase ◽  
Intermediate Formation ◽  
Reduced Form ◽  
Acid Oxidase ◽  
Amino Acid Oxidase ◽  
Cytochrome C Reductase ◽  
Two Stages ◽  
Reduced Forms

Biochemical investigations of the properties of free flavins and of flavoproteins have shown that reduction usually occurs in two stages, with the intermediate formation of semiquinones in the case of free flavins. Flavoproteins often show spectroscopically similar intermediates, when partially reduced with substrate. These may, however, be enzyme-product complexes. Detailed investigation of individual flavoprotein enzymes has shown examples in which catalysis involves transition of the enzyme between oxidized and fully reduced forms (glucose oxidase), between oxidized and intermediate forms (D-amino acid oxidase), and intermediate and fully reduced forms (TPNH—cytochrome c reductase). Further, examples are known in which both intermediate and reduced forms react with oxygen, in which only one reacts, while in TPNH—cytochrome c reductase neither the intermediate nor the reduced form reacts with molecular oxygen. The physiological significance of these complex findings is uncertain, partly because it is not known whether purified flavoproteins occur in the same form in the tissues. It seems unlikely, however, that flavoproteins make a major contribution to the respiratory exchange of mammals.

Occurrence of c-Type Cytochrome in Mycobacterium lepraemurium

1974 ◽  
Vol 52 (11) ◽  
pp. 991-996 ◽  
Author(s):  
M. Ishaque ◽  
L. Kato
Keyword(s):  
Absorption Spectrum ◽  
Cytochrome C ◽  
Cytochrome B ◽  
Antimycin A ◽  
Alpha Band ◽  
Difference Spectra ◽  
Absorption Bands ◽  
Type C ◽  
The Difference ◽  
Mycobacterium Lepraemurium

The existence of c-type cytochrome in Mycobacterium lepraemurium was examined. The dithionite-treated cell-free extracts exhibited absorption peaks of cytochromes a + a3 and b, whereas the alpha band of c-type cytochrome at 552 nm was obscured by the large absorption peak of cytochrome b at 560 nm. The addition of NADH, NADPH, or succinate to cell-free extracts caused the reduction of b- and c-type cytochromes to nearly the same extent and thus the difference spectra displayed distinct separate peaks of b- and c-type cytochromes at 562 and 552 nm, respectively. The cell-free extracts treated with ascorbate showed absorption bands of cytochrome types c and a + a3, whereas the addition of succinate to a system preinhibited by antimycin A revealed the absorption bands of cytochrome b only. The absorption spectrum of the pyridine hemochromogens of M. lepraemurium was similar to that of mammalian cytochrome c. The results clearly indicated that, in addition to cytochromes of the a + a3 and b type, c-type cytochrome is also present in M. lepraemurium.

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