Cytochrome spectral

Another cytochrome c, cytochrome c-550(m), was purified from the bacterium with the aid of the detergent, Triton X-100 (Nomoto et al., 1993). This cytochrome spectrally resembles cytochrome c-550(s), while the N-terminal amino acid sequence differs between them. Its molecular mass is 13.6 kDa. 

Nicholls P, Peterson LC, Miller M, et al. 1976. Ligand-induced spectral changes in cytochrome c oxidase and their possible significance. Biochim Boughs 449 188-196. 

The 8,9- and 10,11-dihydrodiols formed in the metabolism of BA and DMBA respectively are all highly enriched (>90%) in R,R enantiomers (Table III). Labeling experiments using molecular oxygen-18 in the in vitro metabolism of the respective parent compounds and subsequent mass spectral analyses of dihydrodiol metabolites and their acid-catalyzed dehydration products indicated that microsomal epoxide hydrolase-catalyzed hydration reactions occurred exclusively at the nonbenzylic carbons of the metabolically formed epoxide intermediates (unpublished results). These findings indicate that the 8,9- and 10,11-epoxide intermediates, formed in the metabolism of BA and DMBA respectively, contain predominantly the 8R,9S and 10S,11R enantiomer, respectively. These stereoselective epoxidation reactions are relatively insensitive to the cytochrome P-450 isozyme contents of different rat liver microsomal preparations (Table III). 

Recent work in our laboratories has confirmed the existence of a similar pathway in the oxidation of vindoline in mammals (777). The availability of compounds such as 59 as analytical standards, along with published mass spectral and NMR spectral properties of this compound, served to facilitate identification of metabolites formed in mammalian liver microsome incubations. Two compounds are produced during incubations with mouse liver microsome preparations 17-deacetylvindoline, and the dihydrovindoline ether dimer 59. Both compounds were isolated and completely characterized by spectral comparison to authentic standards. This work emphasizes the prospective value of microbial and enzymatic transformation studies in predicting pathways of metabolism in mammalian systems. This work would also suggest the involvement of cytochrome P-450 enzyme system(s) in the oxidation process. Whether the first steps involve direct introduction of molecular oxygen at position 3 of vindoline or an initial abstraction of electrons, as in Scheme 15, remains unknown. The establishment of a metabolic pathway in mammals, identical to those found in Strep-tomycetes, with copper oxidases and peroxidases again confirms the prospective value of the microbial models of mammalian metabolism concept. 

Recently, hf structure associated with the copper signal of cytochrome c oxidase has been reported by Frondsz et al.210 which used octave bandwidth S-band EPR spectroscopy (2-4 GHz). The observed structure has been attributed to copper hfs and to an additional magnetic interaction. Data obtained from powder simulation of the EPR spectra at 2.62 GHz and 3.78 GHz are collected in Table 12.2. In a subsequent paper Frondsz and Hyde211 have shown that in S-band EPR spectra of copper complexes in frozen solutions, improved spectral resolution can be achieved. This new technique, which allows a proper selection of the microwave frequency between 2 and 4 GHz, is therefore recommended for studying powder EPR spectra of these types of compounds. 

Vermilion, J.L. and Coon, M.J. (1978) Purified liver microsomal NADPH-cytochrome P-450 reductase. Spectral characterization of oxidation-reduction states. Journal of Biological Chemistry, 253 (8), 2694-2704. 

Estabrook, R.W., Hildebrandt, A.G., Baron, J., Netter, K.J. and Leibman, K. (1971) A new spectral intermediate associated with cytochrome P-450 function in liver microsomes. Biochemical and Biophysical Research Communications, 42 (1), 132-139. Pompon, D. and Coon, M.J. (1984) On the mechanism of action of cytochrome P-450. Oxidation and reduction of the ferrous dioxygen complex of liver microsomal cytochrome P-450 by cytochrome b5. Journal of Biological Chemistry, 259 (24), 15377-15385. Hildebrandt, A. and Estabrook, R.W. (1971) Evidence for the participation of cytochrome b 5 in hepatic microsomal mixed-function oxidation reactions. Archives of Biochemistry and Biophysics, 143 (1), 66-79. 

Figure 7 Cyclic voltammograms of cytochrome c recorded at different types of pyrolitic graphite electrodes. Also shown are the relative ESCA spectral patterns which show the 0/C ratio in the different treated electrode material (a scale enlargement (x3) is shown for the Ojs peak)...

Cytochrome P-U50 in fish. Cytochrome P-U50 with its characteristic spectral properties has since its discovery been detected in a wide range of organisms including several species of fish (13) Current address... 

Spectral properties of cytochrome P-U50. The spectra of reduced cytochrome P-U50.C0 complex in fish liver microsomes display consistently a peak at U20 nm when the Omura and Sato method (U, ) is used (lL, 19, 22, 27). It would appear that the fish... 

Table II. Comparison of the spectral properties of partially purified little skate liver cytochrome P-l+50 with partially purified rat liver cytochrome P-l+50 and highly purified rat liver cytochro-me P-l+50 and P-1+1+8. ...

Multiple forms of cytochrome P-1+50. It is now clear that there are more than one form of cytochrome P-1+50. Thomas et al. have recently shown by immunochemical means that there are at least six forms of mammalian cytochrome P-1+50 (39) In 1960 s it was noted that there are at least two catalytically and spectrally distinct cytochrome P-l+50 s, viz. cytochrome P-1+50 and cytochrome P-1+1+8 or P -1+50 (1 0, 1 1). Cytochrome P-1+1+8 is inducible by PAH s such as 3-methylcholanthrene (MC) and BP. It metabolizes preferentially PAH s (such as the above carcinogenic inducers). Cytochrome P-1+1+8 derives its name from the fact that when reduced and complexed with carbon monoxide it has an absorbance maximum at 1+1+8 nm. Cytochrome P-1+50 induced by compounds such as phenobarbital (PB) appears similar to the control cytochrome P-1+50 both spectrally and catalytically. 

In addition to the 2 nm shift in the absorption maximum, the two cytochromes can be distinguished by the use of ethyl isocyanide interaction spectra (6, 7) and various inhibitors of the monooxygenase activity (Figure 2 and Table III). The relative magnitude of the ethyl isocyanide-cytochrome P-1+50 interaction spectral peaks at —1+30 and —1+55 nm is pH dependent (6j and if the absorbance differences are plotted as functions of pH, there is a cross-over point at a certain pH which is characteristic for a particular form of cytochrome P-1+50 pH 6.9 for cytochrome P-1+1+8 and pH 7-5-7.6 for PB induced or control cytochrome P-1+50 (6, 21). The cytochrome P-1+50 of apparently uninduced trout species (Salmo trutta lacustris) has been shown by us to have the pH cross-over point for ethyl isocyanide interaction spectrum at pH 7.8 (2l) and the absorption maximum of the reduced trout liver cytochrome P-1+50. 00 complex is 1+50 nm, nevertheless its catalytic and inhibitory properties (2l)(Table III) are similar to those of cytochrome P-1+1+8. 

Figure 2. Spectral properties of Cytochrome P-450s from various sources related to the BF hydroxylase activity, the inhibition of BP hydroxylase, and the extent of covalent binding of BP to DNA.

Ahokas, J.T., Pelkonen, 0. and K rki, H.T. Cytochrome P-1+50 and drug-induced spectral interactions in the hepatic microsomes of a trout sp. Second Congress Hungarian Pharmacological Society, Budapest (1971+) pp 11-ll+. 

In summary, it would appear that rainbow trout are responsive to cytochrome P -450-type inducers (e.g. planar polychlorinated biphenyls and polycyclic aromatic hydrocarbons), but are not responsive to cytochrome P-450-type inducers (e.g. phenobar-bital and non-planar polychlorinated biphenyls). Although induced rainbow trout hemoprotein(s) P-450 show high activity with cytochrome P -450 substrates, the induced hemoprotein at 57,000 daltons appears, in electrophoretic and spectral properties, to differ from rodent cytochrome P -450. 

Hemochromes are the symmetrical bis(ligand) adducts of the Fe11 porphyrins, e.g. the bis(imidazole) moiety [11] presumably occurring in reduced cytochrome a or bs (1, 47). The bis(pyridine) hemochromes Fe(P)Py2 are all rather labile in solution the same is true for the corresponding hemichrome derivatives, [Fe(P)Py2] , which are the cationic oxidation products of the hemochromes. Reliable spectral and other physicochemical data on these species can only be obtained in solution when an excess of L is present to suppress the dissociation equilibrium (5) (M = Fe) (20, 24), which is the origin of subsequent oxidation (n = 0) or solvolysis reactions (n = 0 or 1). 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

The formation of the MV state has been studied using azurin as an electron donor (64, 65). Azurin has the advantage over cytochrome C551 in that even at high concentrations there is little spectral overlap with the Soret or visible region transitions of CCP. The reaction of azurin with CCP under pseudo-first-order conditions is described by two independent exponential processes, with the faster process predominating... 

The biphasic reaction with CO points to the existence of multiple heme-hemopexin conformers, and this is borne out by spectral analyses. The absorbance spectra of rabbit ferri-, ferro-, and CO-ferro-mesoheme-hemopexin are entirely analogous to those of other bis-histidyl heme proteins such as cytochrome 65 142), but the CD spectra exhibit unusual features (Fig. 11). Of particular interest are the weak signal of the ferro complex and the bisignate signal of the CO-ferro complex (also seen in the NO-ferro-mesoheme-hemopexin complex (140) and in human ferri-protoheme—hemopexin (139)). 

Although the heme-binding N-terminal half of NOS bears no sequence similarity to P450s, the spectral properties of the Fe +-CO complex with the characteristic 450 nm Soret maximum (72-74) clearly places NOS in the category of P450-like thiolate enzymes. The architecture of NOS also is strikingly similar to cytochrome P450BM-3 (75)... 

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