Cytochromes absorption spectra

Figure 6.3 (a) Visible absorption spectrum of cytochrome c in its reduced and oxidized states, (b) The three separate a bands in the visible spectrum of beef heart mitochondria (below) indicating the presence of cytochromes a, b and c, with the spectrum of cytochrome c (above) as reference. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)... 

Extensive studies into the association of this cytochrome b with CGD neutrophils were performed by Segal and Jones, and by other workers, in the late 1970s and early 1980s. The cytochrome was completely absent (as determined by the absence of a distinctive absorption spectrum in spectroscopic studies) in almost all cases of X-linked CGD, but present at decreased levels in female relatives of these patients. In almost all cases of autosomal recessive CGD, the cytochrome was present but non-functional, in that it did not become reduced upon cellular activation. This indicated both the heterogeneous nature of the disease and also that some other biochemical defect was responsible for impaired function in these patients. Hence, the search was on for other components of the NADPH oxidase. 

However, in contrast to the human His25Ala HO-l heme complex, which has no detectable activity in the absence of imidazole (78), the His20Ala Hmu O rheme complex in the presence of NAD PH and NADPH-cytochrome P450 reductase was foimd to catalyze the initial meso-hydroxylation of the heme (151). The product of the reaction was Fe verdoheme, as judged by the electronic absorption spectrum and the detection of carbon monoxide as a product of the reaction. Hydrolytic conversion of the verdoheme product to biliverdin and subsequent HPLC analysis confirmed that the oxidative cleavage of the porphyrin macrocycle was specific for the a-meso-carbon. 

Cytochrome a, 36 245 Cytochrome a, 36 245, 249 Cytochrome b 36 429 cyclic voltammogram, 36 354-355 mixtures, cyclic voltammogram, 36 356-357 optical absorption spectrum, 36 418, 420 Cytochrome bjjg, 36 234 Cytochrome b,s2, four-helix bundle arrangement, 46 444... 

ON(SO,)j /0N(S03)2 - redox couple, 33 106 O—O bond, copper proteins, 39 26 homolytic cleavage, 39 60, 62-63 Opposite-spin correlation, 38 439-440 Optical absorption spectrum cytochrome b, 36 418, 420 holoferritin, 36 418-419 Optical centers, interaction with surroundings, 35 319-322... 

Photosystem 1 is basically similar to the photosynthesizing system of bacteria just discussed. The difference between PSl and the photosystem of bacteria lies mainly in the fact that, instead of bacteriochlorophyll P890, the photochemical active centre of PSl contains chlorophyll a as a primary electron donor having the peak in the differential absorption spectrum at 700 nm and thus denoted as P700. In PS2 the primary donor of electrons is a chlorophyll molecule P680 with the peak in the differential optical spectrum at 680 nm. Photosystems 1 and 2 are located close to each other. Between them there is an electron transport chain containing molecules of plasto-quinones and cytochromes. 

The reduction of ring IV in chlorophylls a or b changes the optical absorption spectrum of the molecule dramatically. Whereas the long-wavelength absorption band of a cytochrome is relatively weak (see fig. 14.4), chlorophyll a has an intense absorption band at 676 nm (fig. 14.5). Chlorophyll b has a similar band at 642 nm. Bacteriochlorophylls a and b have strong absorption bands in the region of 770 nm (see fig. 15.5). The chlorophylls thus absorb red or near-infrared light very well. 

Figure 49 (A) Changes in the absorption spectrum, with time, of 1.1 pA/ cytochrome c...

The visible absorption spectrum of a partially purified enzyme of Chromatium vinosum indicates a high-spin cytochrome c (36.49). Whether cytochrome c itself can be regarded as the real enzyme or whether c is only attached to the enzyme during the purification procedure, still remains unclear. On the other hand, Ulbricht (35) could clearty demonstrate that the enzymes of Chromatium gracile and Chromatium minutissimum have no cytochrome character. 

The visible absorption spectrum of oxidised cellobiose oxidase is typical of cytochrome b (Fig. 5-15). The flavin in cellobiose oxidase is weakly fluorescent, with emission maxima at 564 nm and excitation maxima at 380 and 444 nm. There are no obvious transient changes on reduction that can be readily ascribed to flavin semiquinone, but the strong absorbance of the cytochrome would make such changes difficult to detect. 

The absorption spectrum occurs from the ground state. Therefore, it will characterize the electronic distribution in this state. Fluorescence and phosphorescence occur from excited states, and so they are the mirrors of electronic distribution within the excited states, S for fluorescence and T for phosphorescence. Any modification of the electronic distribution in these states, such as in the presence of a charge transfer, will modify the corresponding spectrum. One such example is the reduction of cytochromes. The addition of an electron to the ground state, for example, modifies the electronic distribution within the molecule affecting the absorption spectrum. 

Cytochrome c peroxidase is a special example of a peroxidase for it has as its substrate cytochrome c. Our knowledge of this protein is very largely due to Yonetani and coworkers (76, 77). The absorption spectrum of the protein has bands at 647, 507, and 408 m/t and an infra-red band at 1,000 m/i. The spectrum is in keeping with its being a high-spin/low-spin mixture with about 10% low-spin. The energies of the absorption... 

The absorption spectrum of cytochrome o (128) is also reported in Table 6. In many respects it too is like myoglobin but it reacts with oxygen rather than picking it up. Thus it is a terminal oxidase and not an oxygen carrier. 

The name cytochrome P450 is derived from the fact that these proteins have a haem group and an absorption spectrum characterised by a maximmn absorption wavelength of... 

Little is known about the redox partners of rusticyanin, although a diheme cytochrome, cyt c4, has been imphcated because of its abihty to form a complex with rusticyanin. The complex formation between these two proteins at pH 4.8 induces a dramatic decrease, by almost 100 mV, in the redox potential of rusticyanin, while the potentials of both hemes in the cytochrome remain unchanged. Interestingly, complex formation is also accompanied by changes in the electronic absorption spectrum of rusticyanin that are reminiscent of those observed for the uncomplexed protein at high pH (above pH 7.0) (Giudici-Orticoni et al., 1999). 

The sixth coordination position of the heme iron in cytochrome c peroxidase, which is normally occupied by H2O, is available for reactions with extraneous ligands such as fluoride, cyanide, and azide, as well as substrates and substrate analogs. The acidic-alkaline transition of a hemo-protein, which is caused by the ionization of the bound water ligand, is usually accompanied by significant spectral changes. However, the visible absorption spectrum of cytochrome c peroxidase is not appreciably... 

Altschul et al. (1, B) originally discovered that cytochrome c peroxidase reacts with a stoichiometric amount of hydroperoxide to form a red peroxide compound, which will be referred to hereafter as Compound ES. It has a distinct absorption spectrum, as shown in Fig. 2. The formation of Compound ES from the enzyme and hydroperoxides is very rapid (k, > 10 10 M- sec ). No intermediate, which precedes Com-... 

Figure 1 Visible absorption spectrum of cytochromes in beef heart mitochondria. The mitochondria were suspended at a concentration of 1 mgmL and the reduced minus oxidized difference spectrum recorded. (Figure 5 (p. 14) from Mitochondria A Practical Approach edited by Darley-Usmar et al. (1989). By permission of Oxford University Press)...

Membranes prepared from T. acidophilum oxidize succinate, malate, lactate, and NADH, consuming oxygen in the process, but only contain a single cytochrome. It appears to be a b-type cytochrome based on its absorption spectrum and the solubility of the heme in acid-acetone [126]. Since aeration during growUh affects the cytochrome composition in T. acidophilum, failure to detect a more complex cytochrome pattern may reflect the level of aerobiosis during growth. 

Fig, 3. The optical absorption spectrum of beef liver cytochrome b. The bands at 424, 526, and 557 nm come from the dithionite-reduced protein. The sample conditions were 0,375 mg ml protein 25 mAf phosphate pH 7.4 20°C, The expanded a/fi region shown as an inset has an absorbance scale 2.5 times that of the main spectra. 

N-oxidations, sulfoxidations, dealkylations, deaminations, dehalogenations, and others (Wislocki et al. 1980). These isozymes are responsible for the oxidation of different substrates or for different types of oxidation of the same substrate. Carbon monoxide binds with the reduced form of the cytochrome, forming a complex with an absorption spectrum peak at 450 nm. This is the origin of the name of the enzyme. As a result of the complex, inhibition of the oxidation process occurs. 

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