Heme, hemoglobin

Wheeler KE,Nocek JM, Cull DA,Yatsunyk LA, Rosenzweig AC, Hoffman BM. Dynamic docking of cytochrome b with myoglobin and a-hemoglobin heme-neutralization squares and the binding of electron-transfer-reactive configurations. J Am Chem Soc 2007 129 3906-17. 

J5. Jacob, H. S., and Winterhalter, K. H., The role of hemoglobin heme loss in Heinz body formation studies with a partially heme-deficient hemoglobin and with genetically unstable hemoglobins. J. Clin. Ineest. 49, 2008-2016 (1970). 

FIGURE 24.21 The structure of heme, the prosthetic group of hemoglobin. Heme has a structure similar to that of chlorophyll (Fig. 22.1) in that each is derived from the heterocyclic ring, porphyrin. The iron of heme is in the ferrous (2-f) oxidation state. 

A derivative of porphin. Porphyrin is present in hemoglobin heme is ferroprotoporphyrin, a porphyrin combined with iron (ferro-for Fe. ... 

Hemin is the complex between protoporphyrin and iron in the +3 oxidation state. Iron is in the +2 state in the heme of hemoglobin. The molecule has the following structure ... 

The automated method differs from the ICSH method chiefly in that oxidation and ligation of heme iron occur after the hemes have been released from globin. Therefore, ferricyanide and cyanide need not diffuse into the hemoglobin and methemoglobin, respectively. Because diffusion is rate-limiting in this reaction sequence, the overall reaction time is reduced from approximately three minutes for the manual method to 3 —15 seconds for the automated method. Reaction sequences in the Coulter S + II and the Technicon H 1 and H 2 are similar. Moreover, similar reactions are used in the other Coulter systems and in the TOA and Unipath instmments. 

Synthetic Heme. Synthetic compounds that biad or chelate O2 have been produced. These compounds are commercially attractive because manufacture and Hcensure might be developed as a dmg, rather than as a biological product. It has been shown that synthetic hemes can be used to transfuse animals (53). Although synthetic O2 carriers would avoid the limited hemoglobin supply problem, the synthetic procedures are very tedious, and the possibihty of scale up seems remote. 

PSS-SG composite film was tested for sorption of heme proteins hemoglobin (Hb) and myoglobin (Mb). The peroxidaze activity of adsorbed proteins were studied and evaluated by optical and voltammetric methods. Mb-PSS-SG film on PG electrode was shown to be perspective for detection of dissolved oxygen and hydrogen peroxide by voltammetry with linear calibration in the range 2-30 p.M, and detection limit -1.5 p.M. Obtained composite films can be modified by different types of biological active compounds which is important for the development of sensitive elements of biosensors. 

The most conspicuous use of iron in biological systems is in our blood, where the erythrocytes are filled with the oxygen-binding protein hemoglobin. The red color of blood is due to the iron atom bound to the heme group in hemoglobin. Similar heme-bound iron atoms are present in a number of proteins involved in electron-transfer reactions, notably cytochromes. A chemically more sophisticated use of iron is found in an enzyme, ribo nucleotide reductase, that catalyzes the conversion of ribonucleotides to deoxyribonucleotides, an important step in the synthesis of the building blocks of DNA. 

Lesk and Chothia did find, however, that there is a striking preferential conservation of the hydrophobic character of the amino acids at the 59 buried positions, but that no such conservation occurs at positions exposed on the surface of the molecule. With a few exceptions on the surface, hydrophobic residues have replaced hydrophilic ones and vice versa. However, the case of sickle-cell hemoglobin, which is described below, shows that a charge balance must be preserved to avoid hydrophobic patches on the surface. In summary, the evolutionary divergence of these nine globins has been constrained primarily by an almost absolute conservation of the hydro-phobicity of the residues buried in the helix-to-helix and helix-to-heme contacts. 

Hemoglobin is a tetramer built up of two copies each of two different polypeptide chains, a- and (5-globin chains in normal adults. Each of the four chains has the globin fold with a heme pocket. Residue 6 in the p chain is on the surface of a helix A, and it is also on the surface of the tetrameric molecule (Figure 3.13). 

Hemoprroteins contain heme Hemoglobin Cytochrome e Catalase Nitrate reductase Ammonium oxidase ... 

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