Soret band maximum

Oxyhemoglobin can also undergo minor changes in structure which are apparent in a slight shift of the Soret band maximum absorption first from 414.5 m to about 410 mju, and then to 406 m/u (Jope, 4). It is an interesting feature that hemoglobin reconstituted from heme and free globin also shows maximum absorption at 410 m/u. 

LDMS is particularly well suited for the analysis of porphyrins.35-39 The heme molecule—a 22 rc-electron conjugated protoporphyrin system (Figure 8.1)—is an efficient photo-absorber in the visible and near UV (with an absorption maximum—the Soret band—near 400nm). This feature, concurrently with its low ionization potential, warrants that direct LDMS will possess extremely low limits for heme detection. The uses of IR or UV LDMS for structural characterization of natural porphyrins and their metabolites, synthetic monomeric porphyrins (e.g., used in photodynamic therapy), porphyrin polymers, and multimeric arrays, have been well documented.41148 In addition fast atom bombardment MS has been used to characterize purified hemozoin, isolated from the spleens and livers of Plasmodium yoelii infected mice.49... 

For NP2 and NP3 at pH 7.5, the shift in Soret band positions of the NO complexes for the two oxidation states is somewhat larger—8-10 nm, from 421-423 to 413 nm for the Fe(III) and Fe(II) complexes, respectively (50). However, in contrast to NPl-NO (49) and NP4-NO (50), at pH 5.5 NP2-NO and NP3-NO show very different spectral shifts upon electrochemical reduction, as shown in Fig. 6c for NP3-NO. The Soret band shifts to 395 nm, and both the wavelength maximum and shape of the Soret band are typical of five-coordinate heme-NO centers, including guanylyl cyclase, upon binding NO (53, 54). The reduced forms of both NP2-NO and NP3-NO exhibit similar pH dependence of the absorption spectra, whereas NPl-NO and NP4-NO do not show any pH dependence of their absorption spectra over the pH range 5.5-7.5 (50). 

In comparison to the spectra of the nitric oxide complexes, the optical spectra of the ferric and ferrous forms of NPl-4 in the absence of NO over the pH range of 5.5 to 7.5 show the more typically expected changes in Soretband maximum reported previously for NPl (49). The high-spin NP species have their Soret band maxima at 402-403 nm, whereas the high-spin NP have their Soret band maxima at 430 nm at pH 5.5 for NPl and NP4 and 417-418 nm for NP2 and NP3. In all cases the a, 3 bands are quite broad and of low extinction coefficient (50). 

ZnTPPS/ZnTTAP] (17). It is found that dimerization is accompanied by (a) a blue shift of the Soret band, (b) red shifts of the Q bands, (c) red shift of the fluorescence maximum, and (d) strong quenching of fluorescence. Optical spectra of face-to-face covalently linked diporphyrins show the same trends (20,21). However, in one instance formation of a covalently-linked diporphyrin does not lead to a Soret band shift ( ). Of the systems considered here, [TPPS]2 and [ZnTPPSl2 also fail to show a Soret shift even though the visible absorption bands and fluorescence show clear evidence of dimer formation (10). A summary of observed dimerization induced... 

Figure B3.5.5 Near-UV CD spectra. (A) Bovine a -casein peptide under a variety of conditions (data from Alaimo et al., 1999). Peptide concentration 0.631 mg/ml in 2 mM PIPES, 4 mM KCI, pH 6.75 scan rate 40 sec/nm path length 10 mm bandwidth 1.5 nm. The loss of aromatic dichroism with increasing temperature indicates denaturation, which is, however, not complete at 70°C or in 6 M guanidine hydrochloride. The shift in maximum wavelength indicates loss of tryptophan asymmetry, but less so of tyrosine. (B) Seed coat soybean peroxidase under native and denaturing conditions (data from Kamal and Behere, 2002). Protein concentration 15 pM and path length 10 mm. The negative aromatic band centered around 280 nm and the Soret band around 410 nm both disappear at 90°C, indicating the loss of net conformational asymmetry of the aromatic and heme chromophores.

Clezy and Morrell (61) discuss the appearance of different absorption spectra for a given porphyrin in different solvents and the effect of changing the substituents at the porphyrin perifery. In acetic acid there was only a single Soret maximum at 410—425 nm while in acetone, chloroform, ether and benzene a double Soret band was seen in the region 350—390 nm. It is probable that only one of these bands is really a Soret band and that the higher energy band is probably a forbidden transition. In a similar study, Whitten, Baker, and Corwin (62) examined the... 

Optical absorption spectra of the hydroperoxo-ferric intermediate in HO64 show Soret maximum at 421 nm (5 nm red shifted as compared with 416 nm band for oxy-ferrous HO) and Q-bands at 530 and 557 nm. After annealing at 212-215 K, a new species is formed with Soret band at 406 nm characteristic for the o-meso-hydroxyheme. 

Chromophores free in solution and bound to macromolecules do not display identical s values and absorption peaks. For example, free hemin absorbs at 390 nm. However, in the cytochrome b2 core extracted from the yeast Hansenula anomala, the absorption maximum of heme is located at 412 nm with a molar extinction coefficient equal to 120 mM-1 cm-1 (Albani 1985). In the same way, protoporphyrin IX dissolved in 0.1 N NaOH absorbs at 510 nm, whereas when it is bound to apohemoglobin, it absorbs in the Soret band at around 400 nm. 

C. Blue light excites the Soret band of Chi a, which rapidly becomes deexcited to the lower excited singlet (see Fig. 4.9). Therefore, the energy available is given by the red fluorescence of Chi a (A,max = 666 nm see Fig. 5.3). Consequently, the first compound (A,max = 580 nm) cannot be excited by Chi a. For the pigment with 10 double bonds in conjugation, Equation 4.2 indicates that the absorption maximum occurs at... 

Analogous to the Zn(4-TRPPyP) species, the IPCE values for Zn(4-TRPyP) reach 13 % at maximum absorption (Soret band) of the molecule, much higher than... 

S. acidocaldarius (strain 7) contains a cyanide-sensitive cytochrome oxidase [24], The purified cytochrome (M, 150000) is composed of three subunits (M, 37000, 23 000, and 14000). Difference spectra following reduction with dithionite show a Soret band at 441 nm and a maximum at 603 nm characteristic of aa3-type cytochromes. In addition, there is a band at 558 nm whose connection to the oxidase is not clear. This oxidase is stimulated by cholate, but unlike the oxidase from the DSM 639 strain it is inhibited by low concentrations of cyanide (pM as opposed to mM) and oxidizes horse-heart cytochrome c, TMPD-ascorbate, and caldariella quinol. The rates of oxidation (pmol/min/mg protein) for cytochrome c, TMPD-ascorbate, and quinol are 63, 6.1, and 0.2, respectively. Another cytochrome oxidase that has an absorption maximum at 602 nm, oxidizes caldariella quinol, but does not oxidize cytochrome c, is also present in strain 7 so that the terminal portion of the electron transport system in S. acidocaldarius consists of at least three oxidases. It is suggested [8] that the presence of three oxidases in 5. acidocaldarius is unlikely and that the cyanide-sensitive oxidase was isolated from a different species, namely S. solfataricus. There is little taxonomic information in this assertion to judge whether strain 7 and DSM 639 are indeed different species. However, based on growth conditions reported by the investigators [12,28], which are unique for S. acidocaldarius and S. solfataricus [ 22, there is no reason to suspect that these organisms are different species. 

The first oxidation of the porphyrins H2Por usually leads to corresponding Ti-radical cations that exhibit a hypsochromic shift for the Soret band at half the intensity of the original band. The Q bands are replaced by a structured band system with a maximum at around 650 (see Figure 4.5). The same... 

Since there is reason to believe that hemin also combines with denatured globin (as well as with other proteins), it follows that this nonspecific combination does not involve the same histidine residues. The Soret band of acid hematin in organic solvents and the Soret band of native ferrihemoglobin in water have similar maxima at about 404 m/j but this maximum shifts from 404 m/< to 379 m/t when other proteins are added to the solution of acid hematin. Likewise, when ferrihemoglobin is denatured the absorption maximum of this band in water shifts from 404 to about 370 n t, near its position when hematin is added to other proteins. 

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