Heme compounds, determination

G. N. Sando The Enzymatic Reduction of Ribonucleotides. W. lOosterhuis The Electronic State of Iron in Some Natural Iron Compounds Determination by Mossbauer and ESR Spectroscopy. - A Trautwein Mossbauer Spectroscopy on Heme Proteins. -... 

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. 

Cooking fish decreases the rate of rancid development on storage. This effect is attributed to the destruction of lipoxygenase, formation of water-soluble antioxidants, and destruction of heme compounds. Baked fish developed lower free fatty acids and carbonyl values but higher TBA values than raw fish after storage at -18°C for 8 weeks (Table 11.24). The TBA and carbonyl values reached a maximum and then decreased after 6 weeks storage, apparently because of further decomposition of carbonyl compounds. However, these determinations did not necessarily reflect the degrees of flavor deterioration, which needed to be determined by sensory analyses. 

The Number op Unpaired Electrons per Iron Atom in Some Heme Compounds AS Determined by Magnetic Methods " ... 

Activation parameters for the reaction of NO with metMb, Eq. (15), were determined in this laboratory and in collaboration with van Eldik and Stochel (Table II) (23). Comparison of these activation parameters with those determined for reactions of NO with the water soluble ferri-heme complexes Fem(TPPS)(H20)2 and Feni(TMPS)(H20)2 (Table II) demonstrate that the latter compounds represent reasonable models for the kinetics for the analogous reaction with metMb. For example, the kon step would appear to be defined largely by the H20 lability of metMb(H20), although it is clear that the diffusion through protein channels, the distal residues and the proximal histidine binding to the Fe(III) center must all influence the NO binding kinetics (23,24). These properties may indeed be reflected in the lower AS values for both the on and off reactions on metMb. In a related study, Cao et al. recently... 

The only major difference between compounds I and II is the loss of the anion from the proximal side cavity during the formation of compound II. A subtle change in the location of the heme iron from 0.3 A above the plane to being in the plane of the heme also occurs (97). Whether the loss of the putative anion is simply a reflection of the reduced positive charge on the heme in compound II or the explanation for the inactivation of compound II relative to compound I remains im-determined. 

Other enzyme-based mechanisms. Furthermore, the epimers of artemether showed nearly equal in vivo activity (1.02 mg/kg of body weight for a epimer versus 1.42 mg/kg of body weight for the P epimer), making the heme-based mechanism preferable over the SERCA-based mechanism for which a greater disparity in the activities would be expected. Whatever the situation may be, we all agree that further studies are necessary to clarify, or to unambiguously determine the real mechanism of action of this family of compounds. 

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