Cytochromes spectrum

The cytochromes were first observed by MacMunn as early as 1886. He described their spectral absorption bands in a large variety of organisms and tissues. His discovery was, however, forgotten after a controversy with Huppc-Scyler had raised doubts as to the validity of some of his conclusions, and it was not until 1925 that Kcilin independently rediscovered the remarkable cytochrome spectrum in the flight muscles of a living insect. 

If the DHA-AA system is acting as a respiratory carrier in vivo, then one would expect that the subjection of plant tissues to anaerobic conditions would lead to a fall in concentration, if not to the complete disappearance of DHA. An analogous phenomenon is certainly observed with cytochrome in portions of intact potato tissue. The reduction of cytochrome under anaerobic conditions and its reoxidation on admittance of air may be observed spectroscopically by visual examination of the cytochrome spectrum of the tubers in vivo (Hill and Scarisbrick, 1951). Moreover, these changes are produced quite rapidly within 60 to 90 minutes of the alteration of the atmosphere around the tubers (HiU and Barker, 1951). 

Bands of cytochrome spectrum (TF four bands, BF two bands)... 

Although not discussed in detail here, the normal mode analysis method has been used to calculate the electron transfer reorganization spectrum in / M-modified cytochrome c [65,66]. In this application the normal mode analysis fits comfortably into the theory of electron transfer. 

FIGURE 21.9 Typical visible absorption spectra of cytochromes, (a) Cytochrome c, reduced spectrum (b) cytochrome c, oxidized spectrum (c) the difference spectrum (a) minus (b) (d) beef heart mitochondrial particles room temperature difference (reduced minus oxidized) spectrum (e) beef heart submitochondrial particles same as (d) but at 77 K. a- and /3- bauds are labeled, and in (d) and (e) the bauds for cytochromes a, h and c are indicated. 

Cytochrome P450 monooxygenases are characterized through the presence of the heme (protoporphyrin IX) prosthetic group (Scheme 10.1) that is coordinated to the enzyme through a conserved cysteine ligand. They have obtained their name from the signature absorption band with a maximum near 450 nm in the difference spectrum when incubated with CO. The absorption arises from the Soret Jilt transition of the ferrous protoporphyrin IX-CO complex. 

Figure 5.14 Electrospray spectrum of holocytochrome c". Reprinted from Biochim. Bio-phys. Acta, 1412, Klarskov, K., Leys, D., Backers, K., Costa, H. S., Santos, H., Guisez, Y. and Van Beeumen, 1. 1., Cytochrome c" from the obligate methylotroph Methy-lophilus methylotrophus, an unexpected homolog of sphaeroides heme protein from the phototroph Rhodobacter sphaeroides", 47-55, Copyright (1999), with permission from Elsevier Science.

A decade after the discovery of the Rieske protein in mitochondria (90), a similar FeS protein was identified in spinach chloroplasts (91) on the basis of its unique EPR spectrum and its unusually high reduction potential. In 1981, the Rieske protein was shown to be present in purified cytochrome Sg/complex from spinach (92) and cyanobacteria (93). In addition to the discovery in oxygenic photosynthesis, Rieske centers have been detected in both single-RC photosynthetic systems [2] (e.g., R. sphaeroides (94), Chloroflexus (95)) and [1] (Chlo-robium limicola (96, 97), H. chlorum (98)). They form the subject of a review in this volume. 

Figure 3.7 Time-of flight mass spectrum of cytochrome C.

Figure 3.9 MALDITOF mass spectrum showing over-expressed soluble core domain protein of cytochrome B5.

As noted with the chemotaxonomic studies, the limited resolving power and mass accuracy of MALDI-TOF complicates identification of unknown proteins. If the greatly improved resolving power and accuracy of MALDI-FTMS can be used to monitor overexpressed proteins, it could have significant advantages. Figure 13.12 is a MALDI-FTMS spectrum of E. coli whole cells that have been genetically altered to produce the soluble core domain mammalian cytochrome b5 protein, which consists of 98 amino acids. 

Figure 13.12 9.4 T MALDI-FTMS spectrum of E. coli BL21DE3 overexpressing the soluble core domain cytochrome b5 protein.

FIGURE 4.2 Linewidth increase with temperature for an S = 1/2 system. The linewidth of a feature in the low-spin heme spectrum from cytochrome a in bovine heart cytochrome oxidase has been fit as a convolution of a constant component from inhomogeneous broadening and a temperature-dependent component from homogeneous broadening (Hagen 2006). (Reproduced by permission of The Royal Society of Chemistry.)... 

When one of the Fe-coordinating Ns of the porphyrin is made inequivalent to the others, for example, by pulling on it, or by putting a protein structure around the cofactor, then the molecular x axis and y axis become inequivalent, and the axial EPR spectrum turns into the rhombic spectrum in trace d with derivative trace e (see also Table 5.4). There are now three features in the spectrum a peak, a zero crossing, and a negative peak, and their field positions closely (exactly for zero linewidth) correspond to those of the g-values, gx, gy, and gz. Finally, in trace f of Figure 5.4, which is the experimental X-band spectrum of cytochrome c, it can be seen that not only the g-value (peak position) but also the linewidth is frequently found to be anisotropic. This extra complication will be discussed extensively in Chapter 9. 

A redox reaction is a special case of the equilibrium reaction of A + B in Equation 13.1 B is now a reducible group in a biomolecule with an EPR spectrum either in its oxidized or in its reduced state (or both), and A is now an electron or a pair of electrons, that is, reducing equivalents provided by a natural redox partner (a reductive substrate, a coenzyme such as NADH, a protein partner such as cytochrome c), or by a chemical reductant (dithionite), or even by a solid electrode ... 

Figure 2.21 Electrospray positive ion mass spectrum of cytochrome c, a large molecule...

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