Iron core composition

However, ferritins isolated from the bacterium Pseudomonos aeruginosa (Mann et ah, 1986) and from the chiton Acanthopleura hirtosa (St. Pierre et ah, 1990) have iron cores of limited crystallinity, despite having P Fe ratios of around 1 40, perhaps suggesting that core crystallinity is influenced by the rate of iron deposition as well as by the composition of the medium. The way in which phosphate may influence core development is discussed below. 

Variations in ferritin iron cores include the number of iron atoms, composition, and the degree of order (3,6,21-23). Size variations of the iron core range from 1-4500 Fe atoms and appear to be under biological control (e.g. Ref. 15). The distribution of iron core sizes in a particular ferritin preparation can be easily observed after sedimentation of ferritin through a gradient of sucrose. 

Known compositional variations of ferritin iron cores only Involve phosphate, which can range from as much as 80% (21) to as little as 5% of the iron (21) in normal mammalian liver or spleen, the amount of phosphate in the ferritin iron core is ca. 12% of the iron (24). When the phosphate content is high, the distribution of phosphate is clearly throughout the core rather than on the surface. However, interior locations for phosphate are also suggested when the phosphate content is lower, by data on an Fe(III)ATP model complex (P Fe 1 4) (25) or by phosphate accessibility studies in horse spleen ferritin (P Fe = 1 8) (24). Based on model studies, other possible variations in core composition could Include H2O or sulfate (26). 

Estimates of the Mars core composition by the authors listed above suggest it is made of metal plus iron sulfide, the latter varying from 29 to 44 wt.%. Abundances of siderophile (tungsten, phosphorus, cobalt, molybdenum, nickel) and chalcophile (indium, copper) elements in the mantle (Fig. 13.23) are consistent with equilibrium between sulfide, metal, and mantle silicate at high temperature and pressure (Righter and Drake, 1996). 

Analysis of the nny 82 ammunition as previously detailed shows that it uses a mercuric corrosive primer. Analysis of the Chinese 351/73 ammunition revealed that it has a copper-coated iron-jacketed bullet with an iron core and a lead tip, the cartridge case is steel with a brown colored lacquered finish, a brass primer cup, and the propellant is single based with DPA, 2 x nitrodiphenylamines, camphor, and contains no inorganic additives, and the discharged primer composition is antimony, potassium, chlorine, mercury, tin, sulfur, iron, manganese, phosphorus, zinc, and lead in descending order (lead, antimony, mercury type). 

For a more detailed discussion of ferritin biosynthesis and the possible physiological roles of isoferritins of different subunit compositions, the reader is referred to the recent literature (12, 13, 16, 18-22). In this paper the structures of the iron cores and protein coats of ferritins and the hemoferritins of bacteria are compared and the current state of knowledge concerning mineralization processes in these molecules is discussed in relation to this structural information. 

Chemical Composition of Horse Spleen Ferritin Iron Cores"... 

In detail, an impact of this type, starting with two bodies both with iron cores and silicate mantles, would result in a planet surrounded by a disk of former mantle material. It is from this disk that an iron-depleted Moon would accrete (Canup, 2004). Models of this type are proving highly successful inasmuch as they have the capacity to simultaneously explain the masses of the Earth and Moon, the Earth-Moon angular momentum, and the unusual chemical composition of the Moon. 

Until recently, all ferritin cores were thought to be microcrystalline and to be the same. However, x-ray absorption spectroscopy, Mossbauer spectroscopy, and high-resolution electron microscopy of ferritin from different sources have revealed variations in the degree of structural and magnetic ordering and/or the level of hydration. Structural differences in the iron core have been associated with variations in the anions present, e.g., phosphate or sulfate, and with the electrochemical properties of iron. Anion concentrations in turn could reflect both the solvent composition and the properties of the protein coat. To understand iron storage, we need to define in more detail the relationship of the ferritin protein coat and the environment to the redox properties of iron in the ferritin core. 

Enormous developments in the area of soluble noble metal clusters protected with monolayers are discussed. Mass spectrometry has been the principal tool with which cluster growth has been examined. The composition and chemistry of clusters have been examined extensively by mass spectrometry. Besides gold, silver, platinum, copper and iron clusters have been examined. Clusters have also been examined by tandem mass spectrometry and the importance of ligands in understanding closed shell electronic structure is understood from such studies. Protein protected noble metal clusters belong to a new group in this family of materials. Naked metal clusters bearing the same core composition as that of monolayer protected clusters is another class in this area, which have been discovered by laser desorption ionization from protein templates. 

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