Heme-undecapeptide

The value of the rate constant obtained for the heme undecapeptide, MPll (1.3 x 10 s ), is comparable to... 

Microperoxidase-11, MP-11, is a heme-undecapeptide that is prepared by the digestion of cytochrome c and it includes the active surrounding of cytochrome MP-11 was immobilized on electrode surface s and its electrochemistry was characterized. The MP-11-modified electrodes were reported to act as effective electron mediator interfaces for the reduction of cytochrome c, hemoglobin, myoglobin and nitrate reductase (cytochrome c-dependent). The MP-11-mediated activation of nitrate reductase, NR, was employed to assemble an integrated MP-11/NR electrode for the bioelectrocatalyzed reduction of nitrate (NO3 ) to nitrite (NO2). An affinity complex between a MP-11-functionalized electrode and NR (/Q = 3.7x10 M ) was crosslinked with glutaric dialdehyde to yield the electrically contacted electrode for the bioelectrocatalyzed reduction of nitrate to nitrite. In this system the reduced MP-11 mediates ET to NR and activates the enzyme towards the reduction of NO3. 

As the protein sequence is covalently attached to the heme in cytochrome c, digestion by pepsin gives rise to a heme undecapeptide, and following by tryptic digestion decreases the length of the attached peptide from eleven residues to eight residues, i.e., to a heme octapeptide [12]. These two peptides aggregate in aqueous... 

The large dependence of the Soret-band Cotton effects on the state of oxidation observed in cytochromes c from various mammalian and other sources could not be seen with cytochrome C4 from Azotobacter vinelandii. Its CD spectrum in the range 240—440 nm is rather similar to that of the heme undecapeptide from horse heart cytochrome c (see below). It appears that CD spectra of cytochromes are a better means of characterization and classification than light-absorption spectra (214). 

The value of the rate constant obtained for the heme undecapeptide, MPll (1.3 x 10 s ), is comparable to those of other model compounds.The rate constants for model hemes and the heme c undecapeptide are approximately a factor of 10 larger than those found in cytochromes with 80-90 amino acids. This argues further that the heme exposure to the solvent seems not to be a major factor controlling the rate constants for electron self-exchange in cytochromes. 

CD can be used to monitor the phenomenon of heme isomerism in heme proteins. " The isomerism, discovered by LaMar and co-workers, results from the presence of two forms of myoglobin which differ by 180° in the heme orientation about the a, y-methine carbon axis. The two isomers are present in a 9 1 ratio at equilibrium in carbonmonoxymyo-globin (MbCO) but are in a 1 1 ratio in a sample freshly reconstituted from apomyoglobin and heme. Freshly reconstituted MbCO has a Soret CD band with only about half the amplitude of the native form, " suggesting that the minor isomer (at equilibrium) has only a weak Soret CD spectrum. The major form has a strong positive Soret CD band, whereas the minor form has a weakly negative Soret CD band. These results and the CD of the heme undecapeptide from cytochrome indicate that the origin of the Soret CD band must be more complex than proposed by Hsu and Woody, ... 

CYTOCHROME P-450 LIKE SUBSTRATE OXIDATION CATALYZED BY HEME-UNDECAPEPTIDE, MICROPEROXIDASE-11... 

Microperoxidase-11, MP-11, heme-undecapeptide, prepared by pepsin digestion of cytochrome c, retains the proximal His ligand and two thioether bonds between iron-protoporphyrin IX and two Cys residues. The peroxidase activities of MPs have been demonstrated in the oxidation of so-called peroxidase s substrates, phenolic compounds, in the presence of H2O2. MPs are unique and simple hemoprotein which are not restricted by consideration of the apoprotein structure. In this study, cytochrome P-450-hke reactivities of MP-11, sulfide oxidation, N-dealkylation, and olefin epoxidation, were... 

Some small peptide-heme complexes have been prepared, including an undecapeptide (residues 11-21)668"669 and an octapeptide (residues 14-21). TTiese are useful models as they include the two cysteine residues that covalently link the heme to the peptide, and one of the axial ligands. The axial Met-80 residue is absent, but the position can be filled by methionine or by other ligands as required.670 Work with several octapeptide complexes shows that the rates of outer-sphere electron transfer appear to be independent of the axial ligand, and faster than the reaction for cytochrome c. Other comparisons show that the orientation of the axial methionine in cytochrome c and the contacts between heme and protein are important controlling factors in the electronic structure of the heme. Aqua and hydroxo complexes of iron(III) octapeptide complexes are also useful models for studying spin equilibria in iron(III) hemoproteins.671... 

Harbury HA, Loach PA (1960) Oxidation-linked proton functions in heme octa- and undecapeptides from mammalian cytochrome c. J Biol Chem 235 3640-3645... 

Boehringer catalogue 1982-1983 for enzymes. Sigma catalogue 1983 for MPOases (MPOase 8, 9, or 11 are heme octapeptide, nonapeptide or undecapeptide, respectively)-... 

Figure 8. Absorption spectrum of ferriheme undecapeptide (—) and of ferroheme undecapeptide (hemochromogen) (- ) in 0.05 M sodium tetraborate, pH 9. The right-hand ordinate is for the Soret (y) band and for the absorbances at wavelengths shorter than 210 nm. The hemochromogen bands are labelled a-s. As there are no residues in the undecapeptide with chromophores absorbing at wavelengths greater than 240 nm, the 280 nm, e and S bands are clearly due to the heme chromophore. Reproduced, with permission, from [11],...

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].

Figure 36. Circular dichroism of the Soret (y) band of the ferroheme undecapeptide. Dotted curve, in the presence of imidazole which causes hemes to dissociate with a resulting monomer spectrum that is a simple near-Gaussian curve. The dashed and solid curves are at different stages of association and show at least three bands within the envelope of the simple appearing absorption spectrum (upper curve), which is plotted with respect to the right ordinate. Reproduced, with permission, from [16].

Poly(acrylic acid) (PAA) brushes are also strongly swellable in water, particularly at neutral to basic pH, at which the carboxylic acid moieties are dissociated. Micro- and nanostructured brushes of PAA were prepared on ETFE foils using EUV interference lithography for activation. Microperoxidase 11 (MPl 1) is a heme-containing undecapeptide produced... 

Santucci and co-workers [146] studied microperoxidase , an Fe-porphyrin undecapeptide (MW 1900), pi = 4.7) obtained by hydrolysis of cytochrome c. Cyclic voltammograms, showing diffusion-controlled reduction and oxidation waves, were obtained with a PGE electrode at pH 7. At 25°, E was — 160 mV, i.e. considerably lower than for the intact native protein. This shift was attributed to the far greater solvent exposure for the microperoxidase heme group. By contrast with most electron-transfer proteins, and with behaviour now much more reminiscent of small redox molecules, well-defined electrochemistry was not critically dependent upon electrolyte conditions. There was merely some enhancement of the electrochemical rate (decrease in AEp) upon changing from O.IOM NaC104 to 0.025 M Mg(C104)2. 

Three intermediates are involved in reaction of H2O2 with low-spin iron(III)-heme in which the heme ligand is attached to an undecapeptide fragment. At 22°C and pH 10.4, initial reaction with H2O2 proceeds at a rate of 2.15 x 10 s to yield PlFe 0, which subsequently rear-... 

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