An investigation into thee mechanism of citrate---FE-dependent lipid peroxidation

Chelation by citrate was found to promote the autoxidation of Fe²⁺, measured as the disapperance of 1,10-phenanthroline-chelatable Fe²⁺. The autoxidation of citrate---²⁺ could in turn promote the peroxidation of microsomal phospholipid liposomes, as judged by malondialdehyde formation. At low citrate---Fe²⁺ ratios the autoxidation of Fe²⁺ was slow and the formation of malondialdehyde was preceded by a lag phase. The lag phase evidence of this, linear initial rates of lipid peroxidation were obtained via the combination of citrate---Fe²⁺ and citrate---Fe³⁺, optimum activity occurring at a Fe³⁺---Fe²⁺ ratio of 1:1. Evidence is also presented to suggest that the superoxide and the hydrogen peroxide that are formed during the autoxidation of citrate---Fe²⁺ can either stimulate or inhibit lipid peroxidation by affecting the yield of citrate---Fe³⁺ from citrate---Fe²⁺. No evidence was obtained for the participation of the hydroxyl radical in the initiation of lipid peroxidation by citrate---Fe²⁺.     

亚铁离子对水稻萌发后幼苗生长的促进作用

本文最新报道亚铁离子在远高于营养浓度的情况下（０．４４－７．１６ｍｍｏｌ／Ｌ）能显著促进水稻萌发后的幼苗生长,其效果与已报道的促进因子Ｃ２Ｈ４相当．在试验的１９种不同化合物中,发现只有ＦｅＳＯ４对萌发后水稻幼苗生长有显著的促进作用,并证明其有效成分为Ｆｅ（２＋）．这种促进作用在淹水的厌氧条件下和通气条件均能发生,但通气条件下促进程度稍低．水稻不同基因型对Ｆｅ（２＋）的反应无明显差异,可能这种促进作用是水稻适应水田厌氧环境的方式之一．高浓度乙烯（５０—１００ｐｐｍ）的促进作用与亚铁离子的效果相近．这一发现有助于提高水稻在淹水厌氧直播时的出苗率．－－ｓｉｇｎｉｆｉｃａｎｔａｔｌ％ｌｅｖｅｌ;＊－－ｓｉｇｎｉｆｉｃａｎｔａｔ５％ｌｅｖｅｌ;ｕｓ－－ｎｏｔｓｉｇｎｉｆｉｃａｎｔ．２．３ＥｆｆｅｃｔｏｆｖａｒｉｏｕｓＦｅ＋＋ｃｏｎｃｅｎｔｒａｈｏｎｓｏｎｔｈｅｓｅｅｄｌｉｎｇｇｒｏｗｔｈｏｆｒｉｃｅＴｗｏｇｅｎｏｔｙｐｅｓ,ｍｏｄｅｒｎＩＲ５０ａｎｄｔｒａｄｉｔｉｏｎａｌＡＳＤＩ,ｗｅｒｅｕｓｅｄｆｏｒｆｕｒｔｈｅｒｓｔｕｄｙ．Ｆｅ＋＋ｗｉｔｈｃｏｎｃｅｎｔｒａｔｉｏｎｓｆｒｏｍ０．４４ｔｏ７．１６ｍｍｏｌ／Ｌｗ     

Thermodynamics of heme-induced conformational changes in hemopexin: role of domain-domain interactions.

Hemopexin is a serum glycoprotein that binds heme with high affinity and delivers heme to the liver cells via receptor-mediated endocytosis. A hinge region connects the two non-disulfide-linked domains of hemopexin, a 35-kDa N-terminal domain (domain I) that binds heme, and a 25-kDa C-terminal domain (domain II). Although domain II does not bind heme, it assumes one structural state in apo-hemopexin and another in heme-hemopexin, and this change is important in facilitating the association of heme-hemopexin with its receptor. In order to elucidate the structure and function of hemopexin, it is important to understand how structural information is transmitted to domain II when domain I binds heme. Here we report a study of the protein-protein interactions between domain I and domain II using analytical ultracentrifugation and isothermal titration calorimetry. Sedimentation equilibrium analysis showed that domain I associates with domain II both in the presence and absence of heme with Kd values of 0.8 microM and 55 microM, respectively. The interaction between heme-domain I and domain II has a calorimetric enthalpy of +11 kcal/mol, a heat capacity (delta Cp) of -720 cal/mol.K, and a calculated entropy of +65 cal/mol.K. By varying the temperature of the centrifugation equilibrium runs, a van't Hoff plot with an apparent change in enthalpy (delta H) of -3.6 kcal/mol and change in entropy (delta S) of +8.1 cal/mol.K for the association of apo-domain I with domain II was obtained.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transferrin Modifications and Lipid Peroxidation: Implications in Diabetes Mellitus

Free iron is capable of stimulating the production of free radicals which cause oxidative damage such as lipid peroxidation. One of the most important mechanisms of antioxidant defense is thus the sequestration of iron in a redox-inactive form by transferrin. In diabetes mellitus, increased oxidative stress and lipid peroxidation contribute to chronic complications but it is not known if this is related to abnormalities in transferrin function. In this study we investigated the role of transferrin concentration and glycation. The antioxidant capacity of apotransferrin to inhibit lipid peroxidation by iron-binding decreased in a concentration-dependent manner from 89% at <formula>≥2 mg/ml</formula> to 42% at 0.5 mg/ml. Pre-incubation of apotransferrin with glucose for 14 days resulted in a concentration-dependent increase of glycation: 1, 5 and 13 μmol fructosamine/g transferrin at 0, 5.6 and 33.3 mmol/l glucose respectively, p<0.001. This was accompanied by a decrease in the iron-binding antioxidant capacity of apotransferrin. In contrast, transferrin glycation by up to 33.3 mmol/l glucose did not affect chemiluminescence-quenching antioxidant capacity, which is iron-independent. Colorimetric evaluation of total iron binding capacity in the presence of an excess of iron (iron/transferrin molar ratio=2.4) also decreased from 0.726 to 0.696 and 0.585 mg/g transferrin after 0, 5.6 and 33.3 mmol/l glucose, respectively, p<0.01. In conclusion, these results suggest that lower transferrin concentration and its glycation can, by enhancing the pro-oxidant effects of iron, contribute to the increased lipid peroxidation observed in diabetes.     

Biomineralization of Poorly Crystalline Fe(III) Oxides by Dissimilatory Metal Reducing Bacteria (DMRB)

Dissimilatory metal reducing bacteria (DMRB) catalyze the reduction of Fe(III) to Fe(II) in anoxic soils, sediments, and groundwater. Two-line ferrihydrite is a bioavailable Fe(III) oxide form that is exploited by DMRB as a terminal electron acceptor. A wide variety of biomineralization products result from the interaction of DMRB with 2-line ferrihydrite. Here we describe the state of knowledge on the biotransformation of synthetic 2-line ferrihydrite by laboratory cultures of DMRB using select published data and new experimental results. A facultative DMRB is emphasized ( Shewanella putrefaciens ) upon which most of this work has been performed. Key factors controlling the identity of the secondary mineral suite are evaluated including medium composition, electron donor and acceptor concentrations, ferrihydrite aging/recrystallization status, sorbed ions, and co-associated crystalline Fe(III) oxides. It is shown that crystalline ferric (goethite, hematite, lepidocrocite), ferrous (siderite, vivianite), and mixed valence (magnetite, green rust) iron solids are formed in anoxic, circumneutral DMRB incubations. Some products are well rationalized based on thermodynamic considerations, but others appear to result from kinetic pathways driven by ions that inhibit interfacial electron transfer or the precipitation of select phases. The primary factor controlling the nature of the secondary mineral suite appears to be the Fe(II) supply rate and magnitude, and its surface reaction with the residual oxide and other sorbed ions. The common observation of end-product mineral mixtures that are not at global equilibrium indicates that microenvironments surrounding respiring DMRB cells or the reaction-path trajectory (over Eh-pH space) may influence the identity of the final biomineralization suite.     

Interference of ferric ions with ferrous iron quantification using the ferrozine assay

The ferrozine assay is a widely used colorimetric method for determining soluble iron concentrations. We provide evidence for a heretofore unrecognized interference of ferric ions (Fe^3 +) on ferrous iron (Fe^2 +) measurements performed in the dark. Fe^3 + concentrations affected the absorbance measurements, which linearly increased with incubation time.     

Effect of irrigation with saline magnetized water and different soil amendments on growth and flower production of Calendula officinalis L. plants

Global climate change and increased population caused significant depletion of freshwater especially in arid and semi-arid regions including Saudi Arabia. Saline water magnetization before irrigation may help in alleviating the adverse effects of salinity on plants. The current study aimed to examine the potential beneficial effects of water magnetization and soil amendments on growth, productivity, and survival of Calendula officinalis L. plants. Three types of water (tap water “control”, well water, and magnetized well water) and two types of soil amendments (Fe₂SO₄ and peat moss) were examined. Our results showed that irrigating C. officinalis plants with saline well water (WW) adversely affected growth and flowering as compared to tap water (TW). However, plants irrigated with magnetized water (MW) showed significant enhancement in all the studied vegetative and flowering growth parameters as compared to those irrigated with WW. Furthermore, mineral contents and survival of C. officinalis plants irrigated with MW were higher than those irrigated with TW. Irrigation with MW significantly reduced levels of NA⁺ and Cl⁻ ions in leaves of C. officinalis plants indicating the role of magnetization in alleviating harmful effects of salinity. The current study showed that water magnetization enhanced water quality and increased plant’s ability to absorb water and nutrients. Further studies are needed to examine the possibility of irrigating food crops with magnetized water.     

Nitrosylation of rabbit ferrous heme-hemopexin

Hemopexin (HPX) serves as a trap for toxic plasma heme, ensuring its complete clearance by transportation to the liver. Moreover, HPX-heme has been postulated to play a key role in the homeostasis of nitric oxide (NO). Here, the thermodynamics for NO binding to rabbit ferrous HPX-heme as well as the EPR and optical absorption spectroscopic properties of rabbit ferrous nitrosylated HPX-heme (HPX-heme-NO) are reported. The value of the dissociation equilibrium constant for NO binding to rabbit ferrous HPX-heme (i.e., H) is (1.4±0.2)×10^–7 M, at pH 7.0 and 10.0 °C; the value of H is unaffected by sodium chloride. At pH 7.0, rabbit ferrous HPX-heme-NO is a six-coordinate heme-iron species, characterized by an X-band EPR spectrum with an axial geometry and by =146 mM^–1 cm^–1 at 419 nm. At pH 4.0, rabbit ferrous HPX-heme-NO is a five-coordinate heme-iron species, characterized by an X-band EPR spectrum with three-line splitting centered at 334 mT and by =74 mM^–1 cm^–1 at 387 nm. The pK_a value of the reversible pH-induced six- to five-coordinate spectroscopic transition is 4.8±0.1 in the absence of sodium chloride and 4.3±0.1 in the presence of 1.5×10^–1 M sodium chloride. This result is in agreement with the effect of sodium chloride on rabbit HPX-heme stability. The present data have been analyzed in parallel with those of a related heme model compound and heme-protein systems.     

Isolation and characterization of thermotolerant bacterium utilizing ammonium and nitrate ions under aerobic conditions

A thermotolerant bacterium, identified as Bacillus licheniformis, completely utilized 0.1% (w/v) NH₄NO₃ at 30 and 50°C under aerobic condition. The addition of 0.5 mM Fe²⁺ to the NH₄NO₃ medium markedly promoted the utilization of NH₄⁺ and NO₃⁻. At 50°C, of total nitrogen originally provided, 24% was taken up into the cells and 20% remained in the culture supernatant. Residual nitrogen (56%) was probably removed into the atmosphere. The cell extracts contained enzymes involved in denitrification. GC-MS demonstrated that NH₄ ¹⁵NO₃ had been converted to ¹⁵N₂O. These results indicate that the strain has denitrification ability under aerobic condition.