Heme proteins hemoglobin

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 synthesis and turnover of porphyrins, heme precursors, are important because of the central roles of the heme proteins, hemoglobin, and the cytochromes. Quantitatively, hemoglobin synthesis is a major part of the nitrogen economy in humans. 

The most common dioxygen carriers of nature, the heme proteins hemoglobin and myoglobin, bind Oj in a characteristic structure. The Oj molecule binds to the metal atom through one of its atoms, and the M—O—O unit is angular in shape. Studies on small molecules that bind O2 in this way have concentrated on two classes of ligands, porphyrins and Schiff bases.In the first case, bulky superstructures are usually appended to the porphyrin ligand this superstructure inhibits autoxidation of the metal atom in the... 

Hemerythrin and myohemerythrin have roles as oxygen carriers in marine invertebrates, a function similar to that of the heme proteins hemoglobin and myoglobin in mammals and the copper-protein hemo-cyanin in mollusks and arthropods 1-7, 13). 

Although most of the physiologically relevant states of heme proteins are, in general, not photosensitive, the carbon monoxide adducts of the ferrous forms can be rapidly and efficiently photolyzed and provide a derivative which is ideally suited for the initial photolysis step. Thus, most of the examples discussed in this section involve initial photolysis of these adducts. The initial photoproduct may undergo further bimolecular reactions (with O2, for example) or may simply rebind the photolyzed CO molecule (a reversible reaction) depending on the particular conditions of the experiment. In the interest of brevity and clarity, the examples discussed focus on only two heme proteins hemoglobin and cytochrome-c oxidase. 

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. 

It is estimated that 1 g of hemoglobin yields 35 mg of bihmbin. The daily bihmbin formation in human adults is approximately 250-350 mg, deriving mainly from hemoglobin but also from ineffective erythro-poiesis and from various other heme proteins such as cytochrome P450. 

Fig. 3.1 The molecular structure of heme b (also called protoporphyrin IX), the active center of myoglobin, hemoglobin, catalases, and peroxidases, among other heme proteins. 

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. 

N6. Nyman, M., On plasma proteins with heme or hemoglobin binding capacity. Scand. J. Clin, ir Lab. Invest. 12, 121 (1960). 

The cases of myoglobin and hemoglobin are not rare. Many enzymes are dependent for their function on the presence of a nonprotein group. For example, cytochrome c also contains a prosthetic group similar, but not identical, to heme, as do a number of other proteins. These are known generically as heme proteins. There is a family of enzymes that contain a flavin group, the flavoproteins. Another family contains pyridoxal phosphate, a derivative of vitamin Be. There are a number of other examples. 

In vivo heme is released into the plasma by erythrocyte lysis in the form of hemoglobin and by tissue trauma in the form of myoglobin, and both heme proteins are quickly oxidized to their ferric heme forms (methemoglobin and metmyoglobin) at the oxygen tension found in tissue capillary beds. 

Fig. 1. Overview of intravascular heme catabolism. Hemoglobin, myoglobin, and other heme proteins are released into the circulation upon cellular destruction, and the heme moiety is oxidized by O2 to the ferric form (e.g., methemoglobin and metmyoglobin). Haptoglobin can bind a substantial amount of hemoglobin, but is readily depleted. Ferric heme dissociates from globin and can be bound by albumin or more avidly by hemopexin. Hemopexin removes heme from the circulation by a receptor-mediated transport mechanism, and once inside the ceU heme is transported to heme oxygenase for catabolism.

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