Optical absorption spectrum cytochrome

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... 

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. 

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. 

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. 

There are now good theoretical descriptions of the electronic structures contributing to the optical absorption bands in spectra of porphyrin radicals and ferryl species [160,167] most charge-transfer bands in the latter are due to a transition from a porphyrin p orbital to an Fe-0 tt orbital [167], However, in the absence of a prior knowledge of the structure around the Felv site (and/or spectra of a variety of synthetic model compounds) it is not straightforward to assign an optical spectrum to a ferryl species. Thus the intermediate assumed to be the ferryl species in the binuclear haem c /Cub centre of cytochrome c oxidase [168] has a spectrum at 580 nm essentially identical [169] to that of low-spin ferric haem a3 compounds (e.g. cyanide). 

Fiq. 1. The absorption spectrum of purified beef heart cytochrome b in the reduced form at various temperatures (38). The cytochrome was dissolved in Of)l M sodium phosphate buffer containing 19c deoxycholate at pH 7.4 and a trace of sodium dithionite was added for reduction. The optical path was 3 mm in the case of low temperature spectra and 10 mm in the case of the room temperature spectra. 

This report was complemented by a mediated electrochemistry study using horse cytochrome c as the electron acceptor. This was followed up by an unmediated thin layer optical spectroelectrochemistry study of chicken liver SO using a Au electrode modified by 4-pyridinethiol (Aldrithiol). Reversible changes in the heme absorption spectrum were seen and the caleulated heme redox potential (-115 mV vs. Ag/AgCl) was consistent with previous studies using optical potentiometry and cyclic voltammetry. ... 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

Cyanide can combine with the oxidized form of cytochrome a. However, the oxidized cytochrome a-cyanide complex can be reduced by dithionite or reduced cytochrome c and the resulting spectrum is the same as that of the reduced cytochrome a-cyanide complex which has the same absorption peaks as reduced cytochrome a but the optical den-... 

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