Heme compounds

Peroxidation is also catalyzed in vivo by heme compounds and by lipoxygenases found in platelets and leukocytes. Other products of auto-oxidation or enzymic oxidation of physiologic significance include oxysterols (formed from cholesterol) and isoprostanes (prostanoids). 

The fact that nitrite reacts with the iron of the heme compound was described earlier. Because such a large number of metal ions are present in meat, and because some occur in relatively high concentration, there has been considerable interest in them. For the most part, studies have dealt with how metal ions influence reactions of nitrite. The role of sodium chloride (which is used extensively in meat processing) must also be recognized both in terms of its functional role in making reactants in the meat more or less available, and in terms of reports that it directly influences nitrosation reactions (50). Ando (51) studied the effect of several metal ions on decomposition of nitrite, and in the absence of ascorbate, only Fe++ caused a loss of nitrite but in its presence, the effect of Fe " was more pronounced and Fe+++, Mg++, Ca++ and Zn++ showed similar effects. Lee e al. 

A series of synthetic heme-compounds have been prepared 242, 262, 263) which have the promimal nitrogen base covalently attached to the side-chain on the porphyrin, in a... 

Certain strictly anaerobic bacteria and lactic acid bacteria apparently do not contain heme compounds. In the first named organisms this cannot be ascribed to a failure to perform the first step in porphyrin biosynthesis since Clostridia are notorious for production of the porphyrin-like nucleus (corrin) which occurs in vitamin B12 (7, 43). 

Up to now, two types of iron compounds have been studied with ENDOR, namely heme compounds (hemoproteins and some heme model compounds) and iron-sulfur proteins. For comprehensive summaries of the corresponding EPR work, the reader is referred to the literature234-2371. 

The paper of LoBrutto et al.252 is an interesting example of how the large body of ENDOR data available in heme compounds may be applied to interpret ENDOR spectra of heme systems with less known structure. 

The ENDOR work on heme compounds is an impressive example of a systematic study on an important class of biological compounds. One disadvantage is that most experiments had to be performed with the B0 field parallel to the complex normals, so that the full hfs and quadrupole tensors could usually not be evaluated. A single crystal ENDOR study on aquo-Mb is in preparation to rectify this lack of information257. ... 

The order in which the heme compounds reacted with oxygen was not firmly established nor was the distinction in function between cytochrome c, an electron carrier, and cytochrome oxidase, the enzyme catalyzing the oxidation of ferrocytochrome c by oxygen to give ferri-cytochrome c, (cyt c-Fe3+). 

Iron occurs in every mammalian cell and is vital for life processes. It is bound to various proteins and found in blood and tissues. The iron-porphyrin or heme proteins include hemoglobin, myoglobin and various heme enzymes, such as cytochromes and peroxidases. Also, it occurs in non heme compounds, such as ferritin, siderophilin, and hemosiderin. Hemoglobin, found in the red blood cells, is responsible for transport of oxygen to the tissue cells and constitutes about two-thirds (mass) of all iron present in the human body. An adult human may contain about 4 to 6 grams of iron. 

O Brien, P.J. 1969. Intracellular mechanisms for the decomposition of a lipid peroxide. I. Decomposition of a lipid peroxide by metal ions, heme compounds, and nucleophiles. Can. J. Biochem. 47 485-492. 

Theoeretical models proposed by Griffith (36, 38) and Kotani (59, 60) are now generally employed for the interpretation of the spectral and magnetic properties of hemoproteins. In his recent review Weissbluth (106) gave a detailed account of the calculations involved in these models. The present discussion is limited to a brief outline of the treatment of low spin ferric heme compounds, and the presentation of some results which will be useful for the analysis of the NMR data. 

In paramagnetic molecules with anisotropic g-tensors electron-proton dipole-dipole coupling may contribute to the hyperfine shifts observed in the proton NMR spectra. From the data to be discussed in this section it would seem, however, that in low spin ferric heme compounds many of the qualitative spectral features are mainly determined by Fermitype contact shifts. 

As mentioned at the beginning of this section the size of the pseudocontact shifts in the NMR spectra could in principle be calculated for all the low spin ferric heme compounds if detailed data on the electronic g-tensors were available (Jesson (47)). Unfortunately the EPR data on the azides can not be used directly, because these complexes are not in a pure low spin state under the conditions of the NMR experiments (see section VI C). For the compounds in Figs. 10 through 20 no. successful single-crystal EPR studies were as yet reported. However only g-values determined in frozen solutions are presently available (Blumberg and Peisach (70) Salmeen and Palmer (95a)), e.g. for dicyanoferri-porphin at 1.4 °Kgi = 3.64, g 2.29, and gs 1.0 were found. 

A more detailed treatment, including the effects of spin delocalization on the pseudocontact shifts, might be warranted once single crystal EPR data will become available for several of the low spin ferric heme compounds. In the hemoproteins it would then be of special interest to investigate pseudocontact shifts for amino acid residues near the heme groups which could yield structural information in a similar way as the ring current shifts. 

Eq. (4), which relates the observed contact shifts of the proton resonances to their isotropic contact coupling constants, and hence to the spin densities on the ring carbon atoms, is valid only for systems with isotropic g-tensors. To obtain an estimate of the errors which might arise from its application to low spin ferric heme compounds, we shall briefly consider a more general form of the equation, which was given by Jesson (46) for tetragonal systems with more than one populated electronic state. 

Khan, Z. I. De Rycke, P. H. (1976). Studies on Hymenolepis microstoma in vitro. I. Effect of heme compounds on growth and reproduction. Zeitschrift fur Parasitenkunde, 49 253-61. 

These results and conclusions contrast the suggestion that model heme compounds bind CO much more strongly than do hemoproteins (32). In the solid state, models appear to bind CO irreversibly at room temperature (18, 32), but this is in part due to the high affinity of all hemes, and may, in addition, reflect difficulties in removing the CO from the solid. In solution, models bind CO very strongly... 

Kendrick, J., Watts, B.M. 1969. Acceleration and inhibition of lipid oxidation by heme compounds. Lipids 4, 454-458. 

Koga S, Nakano M, Uehara K (1991) Mechanism for the generation of superoxide anion and singlet oxygen during heme compound-catalyzed linoleic acid hydroperoxide decomposition. J Biolumin Chemilumin 289 223-229... 

HRP exhibits the typical peroxidase fold and active site stractme as shown in Figme 6(b). As with CcP, the native resting form of HRP-C contains a five-coordinate, high-spin Fe + heme. Compound I of HRP contains two oxidizing equivalents, one as oxyferryl (Fe" +-0) and the other as porphyrin radical. " A transient Trp r-cation radical has been detected in the Phe221Trp mutant of HRP-C compound... 

The presence of photosensltlzers In fish oils depends on the method of processing and the source of fish used for rendering. Some species of fish, such as menhaden, which are primarily phytoplankton feeders, can easily contribute residual chlorophyll from their stomach contents when oils are rendered. Fish liver oils have a likelihood of containing residual heme compounds, and thus both oils would be generally more vulnerable to singlet oxygen autoxldatlon than oils recovered from dressed fish. 

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