Increased intracellular iron in mouse primary hepatocytes in vitro causes activation of the Akt pathway but decreases its response to insulin

Background

An iron-overloaded state has been reported to be associated with insulin resistance. On the other hand, conditions such as classical hemochromatosis (where iron overload occurs primarily in the liver) have been reported to be associated with increased insulin sensitivity. The reasons for these contradictory findings are unclear. In this context, the effects of increased intracellular iron per se on insulin signaling in hepatocytes are not known.

Nucleotide sequence of the fhuC and fhuD genes involved in iron (III) hydroxamate transport: domains in FhuC homologous to ATP-binding proteins

Summary The transport of Fe³⁺ into cells of Escherichia coli occurs via siderophores and the uptake through the outer membrane of three Fe³⁺-siderophore compounds containing hydroxamate residues requires three specific receptor proteins. In contrast, transport through the cytoplasmic membrane is catalysed by three common proteins encoded by the fhuB, fhuC and fhuD genes. The nucleotide sequence of a DNA fragment containing the fhuC and fhuD genes has been determined: the open reading frame of fhuC contains 795 nucleotides which encode a polypeptide with a molecular weight of 29 255 and the largest open reading frame of the fhuD region comprises 888 nucleotides. However, we propose that translation of fhuD initiates at the fourth potential start codon resulting in a polypeptide with a molecular weight of 28 282. Both proteins are moderately nonpolar and membrane-bound. They lack obvious signal sequences. Segments of the FhuC protein display strong homology to ATP-binding proteins, suggesting a function in Fe³⁺ uptake similar to the ATP-binding proteins of transport systems that depend on periplasmic proteins. This study completes the nucleotide sequence of the fhu operon which consists of the four genes fhuA fhuC fhuD fhuB arranged in this order on the E. coli chromosome and transcribed from fhuA to fhuB.     

Biochemical genetics of aerobactin biosynthesis in Escherichia coli

Abstract Single-gene mutants of Escherichia coli defective in aerobactin biosynthesis were incubated under non-growing conditions for 2 h with radiolabelled lysine. Analysis of the intermediates produced suggested that acetylation of lysine may be the first step in aerobactin production.     

Characterization of siderophores from Ustilago maydis

Two siderophores, ferrichrome and ferrichrome A, were found in cultures of Ustilago maydis (DC) Corda. Both siderophores were found intracellularly and extracellularly. Their authenticity was confirmed by thin layer chromatography, HPLC, UV-visible spectrometry, paper electrophoresis, amino acid analysis, NMR and fast atom bombardment mass spectroscopy. Regulation of siderophore production by iron was examined. Repression of biosynthesis of extracellular siderophores occurred at 10^–5 M iron. Ferrichrome was found intracellularly at all iron concentrations employed; in general, ferrichrome A was not found to be cell-associated.     

Haemoglobin and Myoglobin as Inhibitors of Hydroxyl Radical Generation in a Model System of “Iron Redox” Cycle

Methionine was oxidized to ethylene by an “Iron Redox” system containing H₂O₂, Fe-EDTA and ascorbate. generating hydroxyl radicals or another species of similar reactivity. Oxy or met forms of haemoglobin and myoglobin were found to inhibit methionine oxidation. Methionine oxidation was elevated in the “Iron Redox” system by increasing ascorbic acid concentration. However, in the presence of metmyoglobin or methaemoglobin, the increases in ascorbic acid did not lower the haemproteins' inhibitory effects but rather increased them.

The pro-oxidative or anti-oxidative activities of haemproteins in biological oxidative reactions seem to be dependent on compartmentalization and on the presence and concentrations of reducing compounds and H₂O₂.     

Effects of root medium pH on root water transport and apoplastic pH in red‐osier dogwood (Cornus sericea) and paper birch (Betula papyrifera) seedlings

• Soil pH is a major factor affecting plant growth. Plant responses to pH conditions widely vary between different species of plants. However, the exact mechanisms of high pH tolerance of plants are largely unknown. In the present study, we compared the pH responses of paper birch (Betula papyrifera) seedlings, a relatively sensitive species to high soil pH, with red‐osier dogwood (Cornus sericea), reported to be relatively tolerant of high pH conditions. We examined the hypotheses that tolerance of plants to high root zone pH is linked to effective control of root apoplastic pH to facilitate nutrient and water transport processes
• In the study, we exposed paper birch and red‐osier dogwood seedlings for six weeks to pH 5, 7 and 9 under controlled‐environment conditions in hydroponic culture. Then, we measured biomass, gas exchange, root hydraulic conductivity, ferric chelate reductase (FCR) activity, xylem sap pH and the relative abundance of major elements in leaf protoplasts and apoplasts.
• The study sheds new light on the rarely studied high pH tolerance mechanisms in plants. We found that compared with paper birch, red‐osier dogwood showed greater growth, higher gas exchange, and maintained higher root hydraulic conductivity as well as lower xylem sap pH under high pH conditions.
• The results suggest that the relatively high pH tolerance of dogwood is associated with greater water uptake ability and maintenance of low apoplastic pH. These traits may have a significant impact on the uptake of Fe and Mn by leaf cells.

     

Carbon- versus sulphur-based zinc binding groups for carbonic anhydrase inhibitors?

A set of compounds incorporating carbon-based zinc-binding groups (ZBGs), of the type PhX (X?=?COOH, CONH₂, CONHNH₂, CONHOH, CONHOMe), and the corresponding derivatives with sulphur(VI)-based ZBGs (X?=?SO₃H, SO₂NH₂, SO₂NHNH₂, SO₂NHOH, SO₂NHOMe) were tested as inhibitors of all mammalian isoforms of carbonic anhydrase (CA, EC 4.2.1.1), CA I–XV. Three factors connected with the ZBG influenced the efficacy as CA inhibitor (CAI) of the investigated compounds: (i) the pKa of the ZBG; (ii) its geometry (tetrahedral, i.e. sulphur-based, versus trigonal, i.e. carbon-based ZBGs), and (iii) orientation of the organic scaffold induced by the nature of the ZBG. Benzenesulphonamide was the best inhibitor of all isoforms, but other ZBGs led to interesting inhibition profiles, although with an efficacy generally reduced when compared to the sulphonamide. The nature of the ZBG also influenced the CA inhibition mechanism. Most of these derivatives were zinc binders, but some of them (sulfonates, carboxylates) may interact with the enzyme by anchoring to the zinc-coordinated water molecule or by other inhibition mechanisms (occlusion of the active site entrance, out of the active site binding, etc.). Exploring structurally diverse ZBGs may lead to interesting new developments in the field of CAIs.     

10-Undecanhydroxamic acid, a hydroxamate derivative of the undecanoic acid, has strong antimicrobial activity through a mechanism that limits iron availability

Undecanoic acid (UDA) is a fatty acid with significant antimycotic activity. In this work we have synthesized 10-undecanhydroxamic acid, a hydroxamate derivative of the UDA, and tested its antimicrobial activity on different microorganisms. Our results demonstrate that this compound has higher efficacy than UDA against a variety of fungi and bacteria. Analysis of the intracellular concentration of protein involved in iron transport in Salmonella enterica serovar Typhimurium suggests that its antimicrobial effect actually relies on the ability to chelate iron ions, providing an efficient mechanism to interfere with microbial growth.     

Peroxynitrite detoxification by ferryl Mycobacterium leprae truncated hemoglobin O

During infection, Mycobacterium leprae is faced with the host macrophagic environment limiting the growth of the bacilli. However, (pseudo-)enzymatic detoxification systems, including truncated hemoglobin O (Ml-trHbO), could allow this mycobacterium to persist in vivo. Here, kinetics of peroxynitrite (ONOOH/ONOO⁻) detoxification by ferryl Ml-trHbO (Ml-trHbOFe(IV)O), obtained by treatment with H₂O₂, is reported. Values of the second-order rate constant for peroxynitrite detoxification by Ml-trHbOFe(IV)O (i.e., of Ml-trHbOFe(III) formation; k_on), at pH 7.2 and 22.0 °C, are 1.5 × 10⁴ M⁻¹ s⁻¹, and 2.2 × 10⁴ M⁻¹ s⁻¹, in the absence of and presence of physiological levels of CO₂ (∼1.2 × 10⁻³ M), respectively. Values of k_on increase on decreasing pH with a pK_a value of 6.7, this suggests that ONOOH reacts preferentially with Ml-trHbOFe(IV)O. In turn, peroxynitrite acts as an antioxidant of Ml-trHbOFe(IV)O, which could be responsible for the oxidative damage of the mycobacterium. As a whole, Ml-trHbO can undertake within the same cycle H₂O₂ and peroxynitrite detoxification.