Mössbauer spectroscopy of iron-containing dermal granules from Molpadia intermedia

Dermal granules containing hydrous ferric oxide cores from Molpadia intermedia were studied by Mössbauer spectroscopy from 1.5 t0 300 K and in magnetic fields up to 80 kOersted at 4.2 K. A magnetic phase transition to an antiferromagnetically ordered state is observed at 10 K. The results are compared with the magnetic behavior of micellar cores of ferritin from eukaryotes and iron-storage materials from prokaryotes.     

Iron plaque enhances phosphorus uptake by rice (Oryza sativa) growing under varying phosphorus and iron concentrations

Both solution culture and pot experiments were performed to investigate (a) the effects of external Fe (II) concentrations and forms on the formation of iron plaque on the roots of rice (Oryza sativa) and subsequent P adsorption on iron plaque and shoot P concentrations and (b) the effects of soil moisture regimes on the formation of iron plaque and P adsorption on root surfaces and P accumulation in shoots. The results showed that iron plaque was significantly increased with increasing Fe²⁺ concentrations in the solution culture. The amounts of P adsorbed on the iron plaque were increased significantly with external Fe²⁺ concentrations. Although shoot P concentration was not significantly affected by Fe²⁺ treatment after incubation for 2 days, it was significantly increased in the Fe‐treated plants compared with Fe‐deprived ones after incubation for 4 days. Soil culture experiment showed that the formation of iron plaque on root surfaces was promoted by exogenous iron, with greater amount of iron plaque being formed by addition of ferric hydroxide than of ferric oxide. Phosphorus adsorption on iron plaque also increased with the addition of iron oxides, and increasing soil P increased the amounts of P associated with the iron plaque and shoot P concentration. The amounts of iron plaque were almost sixfold higher under flooding condition than under field capacity condition. Plants pretreated under flooding condition generally had higher shoot P concentrations when they were transplanted to solutions with varying P levels, and this was most pronounced in the treatment with highest solution P concentration. The results suggest that iron plaque acts as a nutrient reservoir for phosphorus in the rhizosphere and helps enhance P acquisition by rice.     

The ultrastructure of chemolithoautotrophic Gallionella ferruginea and Thiobacillus ferrooxidans as revealed by chemical fixation and freeze-etching

By using sodium thioglycolate to dissolve the high amount of excreted stalk material in axenic cultures of the chemolithoautotrophic iron bacterium Gallionella ferruginea, the ultrastructure of Gallionella cells from pure cell suspensions could be studied without any loss of viability or disturbance by dense ferric stalk fibers, and compared with Thiobacillus ferrooxidans, also grown chemolithoautotrophically with ferrous iron as energy source. Both organisms were chemically fixed or freeze-etched. Particular structural differences between these iron-bacteria could be ascertained. G. ferruginea possesses intracytoplasmic membranes and soluble d-ribulose-1,5-bisphosphate-carboxylase, whereas T. ferrooxidans contains carboxysomes but no intracytoplasmic membranes; Gallionella forms poly--hydroxybutyrate and glycogen as storage material; T. ferrooxidans produces only glycogen. Both organisms also differ from each other with respect to the freeze fracture behaviour of the cell envelope layers. Whereas the cells of T. ferrooxidans exhibit a characteristic double cleavage, exposing the plasmic fracture face and exoplasmic fracture face of the outer membrane and cytoplasmic membrane, the exceptionally thin multilayered cell envelope of G. ferruginea revealed a particularly intimate association between the layers, resulting in a visualisation of the supramolecular organisation of only the inner fracture face of the cytoplasmic membrane. The results are discussed predominantly in relation to the extremely distinct environments of both organisms.     

Soluble and membrane-bound ferrisiderophore reductases of Escherichia coli K-12

After uptake of microbial ferrisiderophores, iron is assumed to be released by reduction. Two ferrisiderophore-reductase activities were identified in Escherichia coli K-12. They differed in cellular location, susceptibility to amytal, and competition between oxygen and ferrichrome-iron(III) reduction. The ferrisiderophore reductase associated with the 40,000×g sediment (membrane-bound enzyme) was inhibited by 10 mM amytal in contrast to the ferrisiderophore reductase present in the 100,000×g supernatant (soluble enzyme). Reduction by the membrane-bound enzyme followed sigmoid kinetics, but was biphasic in the case of the soluble enzyme. The soluble reductase could be assigned to a protein consisting of a single polypeptide of M _r 26000. Reduction of iron(III) by the purified enzyme depended on the addition of NADH or NADPH which were equally active reductants. The cofactor FMN and to a lesser degree FAD stimulated the reaction. Substrate specificity of the soluble reductase was low. In addition to the hydroxamate siderophores arthrobactin, schizokinen, fusigen, aerobactin, ferrichrome, ferrioxamine B, coprogen, and ferrichrome A, the iron(III) complexes of synthetic catecholates, dihydroxy benzoic acid, and dicitrate, as well as carrier-free iron(III) were accepted as substrates. Both ferrisiderophore reductases were not controlled by the fur regulatory system and were not suppressed by anaerobic growth.Abbreviations DHB dihydroxybenzoic acid - MECAM 1,3,5-N,N,N-tris-(2,3-dihydroxybenzoyl)-triamino-methylbenzene - MECAMS 2,3-dihydroxy-5-sulfonyl-derivative of MECAM     

The temporal region and the supramastoid ridge in mesolithic skulls from Padina in the Iron Gate Gorge of the Danube

Studies of the morphological features of the temporal region of mesolithic skulls from Padina in the Iron Gate Gorge of the Danube revealed a very prominent and large supramastoid ridge which is the most striking feature in skulls of both sexes. Mastoid processes were larger in male skulls, but in 25% of the cases there was an overlap between the size of the processes in male and female specimens. The mastoid ridge was prominent in both sexes. The digastric fossa was always well defined in both sexes and in the two thirds of the skull specimens it was deep. The posterior root of the zygoma was prominent in all the skulls, but it was better developed in the male specimens. The parietotemporal suture in both sexes rises above the level of the pterion. There were no morphological or anthropometrical differences between the left and the right side of individual skulls outside the limits of natural asymmetry. All these morphological characteristics of the temporal region may help in racial and sexual diagnosis of the Mesolithic skulls from the Iron Gate Gorge.     

Studies on the role of iron in the reversal of cadmium toxicity in chicks

Studies were conducted to determine the effect of dietary iron (Fe) levels ranging from a deficiency to an excess on the toxicity of cadmium (Cd) in chicks. In Fe-deficient animals, cadmium was found to be more toxic than in Fe supplemented animals as measured by growth. The liver Cd burdens were increased significantly in the presence of dietary Fe supplementation, and there was a significant Cd−Fe interaction in the Cd concentration of the kidney, indicating that iron deficiency increased the concentration of Cd in the kidneys of those chicks receiving this element. Cd tended to reduce the Fe concentration in both the liver and kidney. The absorption of Cd as measured by the amount of¹⁰⁹Cd that disappeared from an isolated duodenal segment in one h was not affected by the Fe content of the diet, but the amount of isotope appearing in the liver compared to the amount present in the blood was increased in the Fe supplemented chicks. Separation of the Cd binding ligands by column chromatography revealed that more of the Cd in the liver, but not the kidney, was associated with ligands which eluted in a column volume that contained metallothionein in those chicks receiving Fe than in the livers from Fe deficient animals. The inverse relationship between the amount of Cd bound to the metallothionein containing fraction and toxicity may be related causally. Paper No. 10538 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601. The use of trade names in this publication does not imply endorsement by the NC Agricultural Research Service of the products named nor criticism of similar ones not mentioned.     

Ferricrocin functions as the main intracellular iron-storage compound in mycelia ofNeurospora crassa

Summary Neurospora crassa produces several structurally distinct siderophores: coprogen, ferricrocin, ferrichrome C and some minor unknown compounds. Under conditions of iron starvation, desferricoprogen is the major extracellular siderophore whereas desferriferricrocin and desferriferrichrome C are predominantly found intracellularly. Mössbauer spectroscopic analyses revealed that coprogen-bound iron is rapidly released after uptake in mycelia of the wild-typeN.crassa 74A. The major intracellular target of iron distribution is desferriferricrocin. No ferritin-like iron pools could be detected. Ferricrocin functions as the main intracellular iron-storage peptide in mycelia ofN. crassa. After uptake of ferricrocin in both the wild-typeN. crassa 74A and the siderophore-free mutantN. crassa arg-5 ota aga, surprisingly little metabolization (11%) could be observed. Since ferricrocin is the main iron-storage compound in spores ofN. crassa, we suggest that ferricrocin is stored in mycelia for inclusion into conidiospores.     

Studies on haemosiderin and ferritin from iron-loaded rat liver

Summary Haemosiderin has been isolated from siderosomes and ferritin from the cytosol of livers of rats iron-loaded by intraperitoneal injections of iron-dextran. Siderosomal haermosiderin, like ferritin, was shown by electron diffraction to contain iron mainly in the form of small particles of ferrihydrite (5Fe₂O₃ · 9H₂O), with average particle diameter of 5.36±1.31 nm (SD), less than that of ferritin iron-cores (6.14±1.18 nm). Mössbauer spectra of both iron-storage complexes are also similar, except that the blocking temperature,T _B, for haemosiderin (23 K) is lower than that of ferritin (35 K). These values are consistent with their differences in particle volumes assuming identical magnetic anisotropy constants. Measurements of P/Fe ratios by electron probe microanalysis showed the presence of phosphorus in rat liver haemosiderin, but much of it was lost on extensive dialysis. The presence of peptides reacting with anti-ferritin antisera and the similarities in the structures of their iron components are consistent with the view that rat liver haemosiderin arises by degradation of ferritin polypeptides, but its peptide pattern is different from that found in human-thalassaemia haemosiderin. The blocking temperature, 35 K, for rat liver ferritin is near to that reported, 40 K, for human-thalassaemia spleen ferritin. However, the haemosiderin isolated from this tissue, in contrast to that from rat liver, had aT _B higher than that of ferritin. The iron availability of haemosiderins from rat liver and human-thalassaemic spleen to a hydroxypyridinone chelator also differed. That from rat liver was equal to or greater, and that from human spleen was markedly less, than the iron availability from either of the associated ferritins, which were equivalent. The differences in properties of the two types of haemosiderin may reflect their origins from primary or secondary iron overload and differences in the duration of the overload.     

Anaerobic growth on elemental sulfur using dissimilar iron reduction by autotrophic Thiobacillus ferrooxidans

Abstract Anaerobic growth on elemental sulfur using dissimilar iron reduction by Thiobacillus ferrooxidans has been demonstrated. The ferric ion reducing activity (FIR) of the anaerobic cells was double that of the aerobic cells. Significant differences in inhibition of FIR by respiratory inhibitors were observed between aerobic and anaerobic cells. A higher amount of cytochrome was detected in anaerobic cells compared to aerobic cells. Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium. The possibility of two different electron transport chains in ferric ion reduction is discussed.