Heme Soret band

The heme in ferric MPO exhibits a relatively strong absorption band near 680 mn, which is responsible for the characteristic green color. The heme Soret band is considerably red-shifted compared to other heme-containing... 

Figure 9. Dramatic hypochromism of the heme Soret band on association of ferriheme octapeptide molecules. Note that the difierence absorbance curves in the lower part of the figure resemble that of Figure 5C (solid curve), and therefore would result from an oblique orientation as shown in Figure 7C. Reproduced, with permission, from [13],...

Figure 10. Hyperchromisra of the heme Soret band of the ferriheme undecapeptide on association. Also observed is a shift of the band intensity to longer wavelengths (red shift). This corresponds to the example in Figure 5B and the head-to-tail (coplanar) orientation of Figure 7B. Reproduced, with permission, from [14].

Linked acid-base equilibrium models explained the pH dependence of the iron heme Soret band visible absorbance, formal potentials, k, and electroactive surface concentrations of Mb in the films [26,37]. The pK of 4.7 in the Mb-lipid... 

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... 

The biochemical activity and accessibility of biomolecule-intercalated AMP clays to small molecules was retained in the hybrid nanocomposites. For example, the absorption spectrum of the intercalated Mb-AMP nanocomposite showed a characteristic soret band at 408 nm associated with the intact prosthetic heme group of the oxidised protein (Fe(III), met-myoglobin) (Figure 8.9). Treatment of Mb with sodium dithionite solution resulted in a red shift of the soret band from 408 to 427 nm, consistent with the formation of intercalated deoxy-Mb. Reversible binding of CO under argon to the deoxy-Mb-AMP lamellar nanocomposite was demonstrated by a shift in the soret band from 427 to 422 nm. Subsequent dissociation of CO from the heme centre due to competitive 02 binding shifted the soret band to 416nm on formation of intercalated oxy-Mb. 

The visible spectra of beef liver catalase (Type A) and its two active peroxide compounds are shown in Fig. 4. The unliganded enz5une has a Soret band at 405 nm (FmM/heme 120) and a characteristic visible... 

The optical spectra of nitrophorins in the absence of added ligands show Soret band maxima at 403-404 nm. On binding NO, the Soret band shifts to 419-420 nm in NPl and NP4, and 421-423 nm in NP2 and NP3 (46, 48-50). Example spectra are shown in Fig. 5a. The direction of the Soret band shift identifies the oxidation state of the heme iron as being Fe(III) (51, 52). The a and (3 bands of the NO complexes are located near 570 and 535 nm, respectively. The histamine complexes have Soret maxima at 410-412 nm and broad a, (3 maxima between 580... 

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). 

The major conclusion of the present study, as can be seen in Figures 1 and 2, is that the primary photodissociating states, in both nitrosyl ferrous and ferric heme complexes correspond to the d - d 2 excitations. The calculated energies also indicate that this dissociative channel can be activated independent of the excitation frequency in the range of Q to Soret band energies. This is the same type of excitation previously identified as the photoactive state involved in CO and O2 photodissociation from ferrous heme complexes. 

The dithionite reduction of the micelle encapsulated aqua (hydroxo) ferric hemes at pH 10 (in inert atmosphere) gives an iron (II) porphyrin complex whose optical spectrum [21] shows two well-defined visible bands at 524 and 567 nm and a Soret band split into four bands (Fig. 10). Such spectral features are typical of four-coordinate iron (II) porphyrins. The magnetic moment (p = 3.8 + 0.2 Pb) of this sample in the micellar solution is also typical of intermediate spin iron(II) system and is similar to that reported for four-coordinate S = 1 iron(II) porphyrins and phthalocyanine [54-56]. The large orbital-contribution (ps.o. = 2.83 p for S = 1) observed in this iron(II) porphyrin... 

Clay/ionic liquid modified electrodes Sun investigated the use of Hb/clay/IL composite MEs for the electrocatalytic detection of HjOj, TCA, and nitrite [43]. The IL [C4CiIm][PFg] (2 mL) was stirred with bentonite clay (1 mg) for 1 h after which 1 mg of Hb was dispersed into the mixture. A volume of this dispersion was then cast onto a freshly polished basal plane pyrolytic graphite (BPPG) electrode. UV-Vis studies revealed the position of the Hb Soret band to be 410 and 412 nm for dry and buffer-immersed films, respectively. This is consistent with a near-native environment surrounding the heme within Hb in the Hb/clay/... 

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.

Our conclusions on the effect of 5-coordination upon the position of the Soret band of reduced metal species can be confirmed by reference to Yonetani and Asakura s work (56) on the spectra of Mn(II) hemes after incorporation of manganese porphyrins into different proteins. In these... 

The theory of the Fe(III) heme spectra has been given in the previous article (52) and in particular the difference between the absorption spectra of high-spin and low-spin species has been stressed. The application of this theory to some proteins has also been described in that article but its purpose was mainly to draw attention to normal spectra. Here we shall point to a number of anomalous spectra especially concerning the movement of the Soret band to much shorter wavelengths than 400 nm. There is a simultaneous notable broadening of this band and a fall in its extinction coefficient. Such effects have frequently been seen in simple model systems and so we deal these first. 

Table 14 gives data on the effect of acidification on the Soret band of a number of proteins. Accompanying the drop in the wavelength there is a decrease in intensity of the band. Directly comparable with this observation is the study of hemes incorporated into polymers by Weight-man (66). His results show that the Soret band moves well below 400 nm... 

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