Heme-related

Sakai T, Morita Y. 1996. Delta-aminolevulinic acid in plasma or whole blood as a sensitive indicator of lead effects, and its relation to the other heme-related parameters. Int Arch Occup Environ Health 68(2) 126-132. 

The biological reduction of nitrate is not heme-related a well-known family of Mo-oxo pterin enzymes facilitate O-atom transfers between nitrite and nitrate, sulfite and sulfate, and other substratesStill, the electrochemical reduction of nitrate on bare metal electrodes is well known, and can also be facilitated by addition of N4 chelates. For instance, Hobbs et al. have examined the electrochemical reduction of nitrate in basic solutions using iron and nickel electrodes coated with phthalocyanin yielding nitrite, hydroxylamine, and ammonia. The iron electrodes efficiency increased when coated with phthalocyanin while the nickel s activity decreased. A related study has been done by Shibata et al. to determine the synthetic applications of simultaneous reduction of nitrate and carbon dioxide using phthalocyanin complexes of most of the first-row transition metals and other metals with mixed success . 

In this chapter, I have tried to summarize the current applications of different EPR techniques in the study of low- and high-spin ferric heme proteins, NO-ligated heme systems, and spin-labeled heme proteins, with emphasis on the use of ENDOR and pulse-EPR techniques in a multifrequency approach. Note that there are many other heme-related centers that were not dealt with in this chapter, such as the very nice work of the Hoffman group on the cryoreduced heme centers in cytochrome P450cam [89,90]. This chapter should therefore not be seen as a full review of all EPR work on heme proteins, not even for those themes that were specifically selected. I have merely tried to give examples of the different EPR tools that are currently used in heme research. 

The production of NO by NO-synthase (NOS) (Figure 12) involves two domains, a reductase which binds flavin and an oxygenase which comprises a heme unit to which the substrate L-arginine binds. Three different forms of NOS are known, an inducible (iNOS), an endothelial (eNOS) and a neuronal one (nNOS). The details of the arginine oxidation mechanism have been studied in recent years, but only at the level of free-radical formation as far as EPR is concerned, so that the heme related part has not been addressed in great detail since the last review. The free-radical part involves determination of not only NO but also the superoxide anion and the tetrahydrobiopterin radical, to name the most prominent representatives. For the purpose of the present context we only mention briefly some of the relevant investigations. The production of O2 from the nNOS oxygenase domain was reported, as was its release by iNOS and by eNOS. A review on this aspect has become available. The role of NO in relation ofNO and ONOO has been reviewed with respect to consequences in postischemic myocardium. The detection of the tetrahydrobiopterin radical in the first reaction cycle of eNOS and nNOS has been reported. The interplay... 

Delta aminolevulinic-acid dehydratase (ALAD) is perhaps the most widely studied heme-related enzyme that is altered by metal contamination. ALAD conjugates two aminolevulinic acid molecules critical to heme biosynthesis. The zinc-dependant enzyme is easily inhibited by lead substitution and has been extensively characterized as a sensitive indicator of lead exposure. Blood is the ideal matrix for assessing ALAD activity in wildlife, and sampling is easy and non-lethal. Decreased ALAD activity has been correlated to lead accumulation in a wide variety of birds such as waterfowl, game birds, raptors, and passerines (28, 42, 53, 54, 90-92). 

Allen GC, Warren KD (1974) The Electronic Spectra of the Hexafluoro Complexes of the Second and Third Transition Series. 19 105-165 Alonso JA, Baibas LC (1993) Hardness of Metallic Clusters. 80 229-258 Alonso JA, Baibas LC (1987) Simple Density Functional Theory of the Electronegativity and Other Related Properties of Atoms and Ions. 66 41-78 Andersson LA, Dawson JH (1991) EXAFS Spectroscopy of Heme-Containing Oxygenases and Peroxidases. 74 1-40 Antanaitis BC, see Doi K (1988) 70 1-26... 

Tofield BC (1975) The Study of Covalency by Magnetic Neutron Scattering. 21 1-87 Trautwein AX, Bill E, Bominaar EL, Winkler H (1991) Iron-Containing Proteins and Related Analogs-Complementary Mossbauer, EPR and Magnetic Susceptibility Studies. 78 1-96 Trautwein AX (1974) Mossbauer-Spectroscopy on Heme Proteins. 20 101-167 Tressaud A, Dance J-M (1982) Relationships Between Structure and Low-Dimensional Magnetism in Fluorides. 52 87-146... 

The biochemistry of the porphyrins and of the bile pigments is presented in this chapter. These topics are closely related, because heme is synthesized from porphyrins and iron, and the products of degradation of heme are the bile pigments and iron. 

If the enzyme lesion occurs early in the pathway prior to the formation of porphyrinogens (eg, enzyme 3 of Figure 32-9, which is affected in acute intermittent porphyria), ALA and PBG will accumulate in body tissues and fluids (Figure 32-11). Glinically, patients complain of abdominal pain and neuropsychiatric symptoms. The precise biochemical cause of these symptoms has not been determined but may relate to elevated levels of ALA or PBG or to a deficiency of heme. 

Various minor hematological effects have been noted in animals. Rats exposed to 50-800 ppm of trichloroethylene continuously for 48 or 240 hours showed time- and dose-related depression of delta-aminolevulinate dehydratase activity in liver, bone marrow, and erythrocytes (Fujita et al. 1984 Koizumi et al. 1984). Related effects included increased delta-aminolevulinic acid (ALA) synthetase activity, reduced heme saturation of tryptophan pyrrolase and reduced cytochrome P-450 levels in the liver and increased urinary excretion of... 

Although impressive progress has been made in unraveling the mechanism of ORR catalysis by cofacial porphyrins, much remains to be learned before we can understand how this mechanism relates to those in heme enzymes and simple metalloporphyrins and use our mechanistic knowledge to rationally design improved metalloporphyrin catalysts for the ORR. 

Fig. 9.10 Dynamic stractural disorder of the terminal oxygen in oxymyoglobin between positions 1 and 2 which are related via a rotation by 40° about the heme normal...

Alterations in blood heme metabolism have been proposed as a possible indicator of the biological effects of hydrogen sulfide (Jappinen and Tenhunen 1990), but this does not relate to the mechanism of toxicity in humans. The activities of the enzymes of heme synthesis, i.e., delta-aminolevulinic acid synthase (ALA-S) and heme synthase (Haem-S), were examined in 21 cases of acute hydrogen sulfide toxicity in Finnish pulp mill and oil refinery workers. Subjects were exposed to hydrogen sulfide for periods ranging from approximately 1 minute to up to 3.5 hours. Hydrogen sulfide concentrations were considered to be in the range of 20-200 ppm. Several subjects lost consciousness for up to 3 minutes. 

The data from the only available animal study (Prigge and Greve 1977) indicate that inhaled lead is not teratogenic. However, it impaired heme synthesis in both rat dams and fetuses. In this study, dams were exposed to 1, 3, or 10 mg lead/m3 (chemical species not provided) throughout gestation (days 1-21). Maternal and fetal ALAD were inhibited at all exposure levels in a dose-related manner, and fetal (but not maternal) hematocrit and body weight were decreased at the 10-mg/m3 lead level. These results suggest that the fetuses were more sensitive to lead-induced toxicity than were the dams. 

Health effects that have been associated with lead exposures during infancy or childhood include, anemia (Schwartz et al. 1990) (and related disorders of heme synthesis), neurological impairment (e.g., encephalopathy), renal alterations, and colic (Chisolm 1962, 1965 Chisolm and Harrison 1956), and impaired metabolism of vitamin D (Mahaffey et al. 1982 Rosen and Chesney 1983). Death from encephalopathy may occur with PbB levels 125 pg/dL. In addition to the above effects, the following health effects have been associated with lead exposures either in utero, during infancy or during... 

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