Heme, structure

The fragment ions at m/z 571,557,526,512,498, and 484 correspond to consecutive cleavages of 45 (COOIF), 59 (CHT OOIF) or 73 (CH2CH2COOH ) from M+ that are directly correlated with the heme structure. Hemin, synthetic (l-hematin (heme crystals), and parasite-derived heme crystals yield... 

HRP is a hemoprotein containing photohemin IX as its prosthetic group. The presence of the heme structure gives the enzyme its characteristic color and maximal absorptivity at 403 nm.The ratio of its absorbance in solution at 403 nm to its absorbance at 275 nm, called the RZ or Reinheitzahl ratio, can be used to approximate the purity of the enzyme. However, at least seven isoenzymes exist for HRP (Shannon et al., 1966 Kay et al., 1967 Strickland et al., 1968), and their RZ values vary from 2.50 to 4.19. Thus, unless the RZ ratio is precisely known or determined for the particular isoenzyme of HRP utilized in the preparation of an antibody-enzyme conjugate, subsequent measurement after crosslinking would yield questionable results in the determination of the amount of HRP present in the conjugate. 

FIGU RE 22.21 The heme structure with a molecule of oxygen attached. Note the angular orientation of the oxygen molecule and that the Fe... 

When an oxygen molecule is attached to the iron in the heme structure, the Fe2+ changes from high spin to low spin, but the iron remains in the +2 oxidation state. In the heme structure, the Fe2+ ion resides above the plane of the four nitrogen atoms in the porphyrin structure, and an imidazole group is attached to the iron on the side away from the plane of the four nitrogen atoms. This structure is shown in Figure 22.20. 

Keywords Design, Polypeptide, Catalysis, Metalloprotein, Heme, Structure, Protein folding, Glycopeptide. 

Fig. 10. a-meso-Methyl-substituted heme groups and their oxidation to biliverdin products. The substituent R in the heme structure is a methyl in the symmetric porphyrin and an ethyl in mesoheme. 

The differences that we see in the picosecond photodissociation between the natural and synthetic complexes may be linked to important structural differences in the heme pocket or constraints on the tertiary geometry of the heme imposed by the protein. In particular we would like to comment on the proximal imidazole. Recent theoretical ( ), x-ray structural ( ), and resonance Raman work (6-10) all suggest that the affinity of the sixth axial-ligand for the heme is critically dependent on the tertiary heme structure that originates from the linkage of the imidazole to the heme. In the natural complexes, this imidazole (His F8) and the F helix to which it is bound undergo major structural movements these changes for the a... 

The n values of the PLL-ferriheme and -ferroheme complexes in Table 4 are equal to 2, and the six-coordinate heme structure is formed preferentially this may be due to an inherent factor in which PLL differs from the other polymer ligands. 

When a protein possesses a prosthetic group such as heme, its concentration is usually determined at the absorption wavelengths of the heme. The most important absorption band of heme is called the Soret band and is localized around 408-425 nm. The peak position of the Soret band depends on the heme structure, and in cytochromes, this will depend on whether cytochrome is oxidized or reduced. 

Pig. 5.9 Mechanism proposed for formation of a covalent bond between a heme methyl and a protein carboxyl group. A similar sequence must occur again to form the second heme-protein ester link in the mammalian peroxidases. In the heme structure, V stands for -CH=CH2 and P for... 

Chemically modified myoglobin and residues with small-sized substituents not containing reactive groups. In contrast, electron-rich substituents disrupted the heme structure The modification rates were slower for [61]... 

Sitter AJ, Reczek CM, Temer J (1986) Comparison of the heme structures of horseradish peroxidase compounds X and II by resonance Raman spectroscopy. J Biol Chem 261 8638-8642... 

Carbon monoxide is extremely toxic because it complexes with iron in the heme structure in the blood. When it binds to the iron, it binds more strongly than an 02 molecule, so the CO destroys the oxygen-carrying capability of the blood. Many deaths occur annually as a result of this behavior. 

Current evidence indicates that hypervalent iron complexes—ferryl iron (FelV, Fe02, Fe(IV)=0) or perferryl iron (FeV)—are involved in the catalytic mechanism, but there is stiU controversy over the details of reaction mechanisms and what proportion of heme catalysis it accounts for. Very recently, some very elegant chemistry has elucidated binding and 0—0 bond scission mechanisms and identified heme structural elements critical for oxidation catalysis (143, 144). Paradoxically, although the early theories of heme catalysis have been largely dismissed, they nevertheless are consistent with aspects of hypervalent iron behavior. Ferryl iron chemistry encompasses and explains the most important features noted in early studies (99) ... 

The redox sensitivity of hemopexin-encapsulated heme to electrolyte composition and pH illustrate the importance of first coordination shell (bis-histidine ligation and heme structure) and second coordination shell (protein structure/folding and environment) effects in these heme proteins. These observations also suggest a possible role for Fe " /Fe redox in hemopexin-mediated heme transport/recycling, as high chloride anion concentration and low pH are known conditions for the endosome where the heme is released. 

Phagocytic breakdown destroys older blood cells, primarily in the spleen, but also in the marrow (Fig. 99-2). Amino acids from the globin chains return to an amino acid pool heme oxygenase acts on the porphyrin heme structure to form biliverdin and to release its iron. Iron returns to the iron pool to be reused while biliverdin is further catabolized to bilirubin. The bilirubin is then released into the... 

Heme structure. The chemical structure of heme shows the ferrous iron in the center with the hydrophobic surroundings and the two polar propionic acid groups at the top. 

Figure 8.19 The substrate, testosterone, (in red) is shown within the active site of CYP3A4. Hydrogen bonds are dashed iines. The heme structure is shown in the bottom piane. (From DFV Lewis, Univ Surrey. Figure is Fig 6 from Xenobiotica 34 549-569, 2004.)...

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