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PubMed1995

Inhibition of adenylyl cyclase in rat striatal homogenates by combinations of dopamine and ferric iron compounds.

The adenylyl cyclase activity of homogenates of striatal tissue from rat brain has been used as a model to test the hypothesis that the products of the reaction of polyphenols with ferric iron compounds are toxic. Dopamine (DA), at levels that stimulate adenylyl cyclase, inhibited the activity in the presence of 2 mol of potassium ferricyanide (FC), methemoglobin or ferricytochrome c per mol of DA. Combinations of potassium ferrocyanide and DA were not inhibitory. Neither pyrocatechol nor hydroquinone stimulated the activity, but these polyphenols were inhibitory in the presence of FC. Tyramine, phosphorylated DA or phosphorylated pyrocatechol had no effect on the activity of the enzyme in the presence or absence of FC. Forskolin was unable to stimulate the adenylyl cyclase once the latter was inhibited by DA plus FC, and dithiothreitol could not reverse inhibition by DA plus FC. Incubation of DA with FC, in the absence of the homogenate, resulted in substances that were not inhibitory. These findings suggest that the polyphenols plus FC react to yield substances that inhibit the adenylyl cyclase by affecting the catalytic unit of the enzyme complex.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2001

[The effects of iron compounds on SO2 and NO emissions in coal combustion process].

The effects of ferric/ferrous chlorides and ferric oxide on emissions in Tongchuan coal combustion process were experimentally investigated using thermogravimetric analyzer. The results show that all iron compounds used in the experiments, namely FeCl3, FeCl2 and Fe2O3 can change the emissions of SO2 and NO, but with different mechanisms and different magnitudes. FeCl3 plays the roles of both a catalyst and an absorbent in the conversions from coal-S to SO2 and from coal-N to NO. Due to the catalysis the activation energy required for the formation of SO2 and NO is reduced, the rates of the reactions leading to SO2 and NO increased. The catalysis is concerned with the forms of coal sulfur. Due to the absorption FeCl3 reacts with SO2 to produce FeSO4 [symbol: see text] Fe2(SO4)3. In addition FeCl3 can decrease the emissions of CO, i.e., the combustion characteristics can be changed. The effects of FeCl2 on the emissions of SO2, NO and CO are similar to those of FeCl3, but weaker. Fe2O3 can also decrease the SO2 and NO emissions to some extent, but has negligible influence on CO emission.

Catalysis↗
PubMed2001

The X-ray absorption spectroscopy Debye-Waller factors of an iron compound and of met-myoglobin as a function of temperature.

Protein dynamics can be characterized by the mean square displacements of the individual atoms of a molecule. This concept is extended to X-ray absorption spectroscopy (XAS) of proteins where the physical information in the Debye-Waller factor is in general neglected. In a first step, a procedure for the investigation of the temperature dependence of XAS spectra has been developed for a small iron compound. Subsequently, experiments have been performed on met-myoglobin. It is shown that the mean square displacements of XAS are smaller than those obtained by Mössbauer spectroscopy and far smaller than crystallographic mean square displacements. This behavior is explained by the different sensitivity of the methods. XAS measures a relative mean square displacement between the absorbing and backscattering atoms only. A comparison with mean square displacements calculated from normal modes shows that static displacements contribute significantly. It becomes obvious that the atoms of the active center show a high correlation of their motions.

Binding Sites↗
PubMed1976

Factors affecting the susceptibility of staphylococci to killing by the cationic proteins from rabbit polymorphonuclear leucocytes: the effects of alteration of cellular energetics and of various iron compounds.

Anaerobiosis, various respiratory inhibitors and certain agents altering cellular energetics profoundly affect the staphylocidal action of the cationic proteins from rabbit polymorphonuclear leucocytes. It is suggested that sensitivity to these proteins depends on the structure of the cell membrane as influenced by (1) the oxidation level of the cytochrome chain and (2) its energized state. Agents such as amytal and rotenone, which cause a block at the beginning of the chain and would increase its oxidation level, enhance killing, whereas those causing a block in or at the end of the chain, such a 2-n-heptyl-4-hydroxyquinoline-N-oxide, cyanide and anaerobiosis, which would cause reduction of a part or whole of the chain, prevent killing. Among agents altering the energized state of the membrane, dicyclohexyl-carbodi-imide, an ATPase inhibitor, does not prevent killing, whereas 2,4-dinitrophenol, carbonylcyanide-trifluoromethoxy-phenylhydrazone and 5-Cl, 3-t-butyl, 2'-Cl, 4'-NO2-salicylanilide, all uncouplers and ionophores for a specific ion, do prevent killing, although gramicidin, a relatively nonspecific ionophore, does not. The paper also contains an extension of previous work on the effect of iron and haematin, to include various other iron compounds and haematin derivatives.

Amobarbital↗
PubMed1988

Accumulation of iron and iron compounds in liver tissue. A comparative study of the histological and chemical estimation of liver iron.

Unsatisfactory results obtained by histological evaluation of liver tissue in iron loading diseases prompted us to study the distribution of the total liver iron, haem iron and ferritin iron in post mortem human liver tissue from two different sites of the same liver. The total liver iron content was measured by flameless atomic absorption spectroscopy in native liver homogenates and in acid digested liver tissue from 60 consecutive autopsies, and the results from the two methods were compared. From the standard deviation of the duplicate analyses, it was deduced that the liver iron is possibly inhomogeneously distributed. The CVduplo (22%) of total iron, measured in acid digested tissue was higher than the CVduplo (14%) of total iron in homogenates from liver tissue from which non-homogenized tissue e.g. vessel walls, fibrotic tissue, had been removed. The CVduplo of ferritin iron and haem iron in liver homogenate was 14% and 30% respectively. The ferritin iron increased with an increasing total iron content until saturation of ferritin iron appeared to be reached at 2.5 micrograms ferritin iron per mg liver protein. When the results of total non-heam liver iron measurements are expressed properly (amount of iron per amount of homogenized liver protein), the distribution of iron is found to be homogeneous in both normal and pathological liver tissues. It was concluded that the estimation of liver iron content by visual microscopic evaluation is unsatisfactory, and that more reliable results are obtained by atomic absorption spectrophotometry.

Ferric Compounds↗
PubMed1976

Observations and interpretation of x-ray absorption edges in iron compounds and proteins.

X-ray absorption spectra near the Kalpha edge have been measured in various iron group compounds using the intense synchrotron radiation at the Stanford Synchrotron Research Project. In the cubic compounds KMF3 where M = Mn+2, Fe+2, Co+2, Ni+2, and Zn+2, well resolved lines were observed and assigned to the 1s leads to 3d, 1s leads to 4s, and 1s leads to 4p transitions. The observed energies agreed rather well with the spectroscopic energy levels of the Z + 1 ion and the intensities are shown to agree with those expected on the basis of one electron transitions of the form Z 1s2dn(L,S) leads to (Z + 1)1s2dnn'l'(L",S). The energies of the intense 1s leads to 4p transition increase by about 5 V going from KFeF3 to K2NaFeF6, but only by about 1 V from K4Fe(CN)6 to K3Fe(CN)6. The transitions confirm that upon oxidation of the hexacyanides the iron electronic structure barely changes. In the iron sulfur protein rubredoxin, where the iron is bound to a tetrahedron of sulfurs, the 1s leads to 3d transition was about seven times more intense than the same transition in an octahedrally coordinated compound. These intensities parallel those observed in the d-d transitions of optical spectra, because in both types of spectra the intensities depend upon 4p admixture. In the heme protein cytochrome c, upon oxidation the 1s leads to 4p transition shifts only about 1 V to higher energies similar to the iron hexacyanides. These results are discussed in terms of covalent bonding.

Cytochrome c Group↗