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Small Angle X-Ray Scattering

The ferritins: molecular properties, iron storage function and cellular regulation☆

Based on fundamental chemistry, biotechnology and materials science have developed over the past three decades into today's powerful disciplines which allow the engineering of advanced technical devices and the industrial production of active substances for pharmaceutical and biomedical applications. This review is focused on current approaches emerging at the intersection of materials research, nanosciences, and molecular biotechnology. This novel and highly interdisciplinary field of chemistry is closely associated with both the physical and chemical properties of organic and inorganic nanoparticles, as well as to the various aspects of molecular cloning, recombinant DNA and protein technology, and immunology. Evolutionary optimized biomolecules such as nucleic acids, proteins, and supramolecular complexes of these components, are utilized in the production of nanostructured and mesoscopic architectures from organic and inorganic materials. The highly developed instruments and techniques of today's materials research are used for basic and applied studies of fundamental biological processes.

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Nanoparticles, Proteins, and Nucleic Acids: Biotechnology Meets Materials Science

http://leung.uwaterloo.ca/MNS/102/Lectures%202007/SSNT-1-Introduction_files/Images/ferritin%20article.pdf

Mineralization in ferritin: an efficient means of iron storage.

Ferritin has a high capacity as an iron store, incorporating some 4500 iron atoms as a microcrystalline ferric oxide hydrate. Starting from apoferritin, or ferritin of low iron content, Fe(2+) and an oxidizing agent, the uptake of iron can be recorded spectrophotometrically. Progress curves were obtained and the reconstituted ferritin was shown by several physical methods to be similar to natural ferritin. The progress curves of iron uptake by apoferritin are sigmoidal; those for ferritins of low iron content are hyperbolic. The rate of iron uptake is dependent on the amount of iron already present in the molecule. The distribution of iron contents among reconstituted ferritin molecules is inhomogeneous. These findings are interpreted in terms of a crystal growth model. The surface area of the crystallites forming inside the protein increases until the molecule is half full, and then declines. This surface controls the rate at which new material is deposited. The experimental results can best be accounted for by a two-stage mechanism, an initial slow ;nucleation' stage, which is apparently zero order with respect to [Fe(2+)], followed by a more rapid ;growth' stage. The rate of Fe(2+) oxidation is increased in the presence of apoferritin as compared with controls. Ferritin can therefore be regarded as an enzyme to which the product remains firmly attached. The protein appears to increase the rate of ;nucleation'. The apparent zero order of this stage suggests the presence of binding sites on the protein, which are saturated with respect to Fe(2+). These sites are presumed also to be oxidation sites. The oxidation and subsequent formation of the ferric oxide hydrate may proceed according to one of three alternative models.

The formation of ferritin from apoferritin. Kinetics and mechanism of iron uptake

On the structure of hemosiderin and its relationship to ferritin.

Iron uptake and release by ferritin molecules of different iron contents show similar profiles. These are discussed in relation to the structure of the ferritin molecule. Two models of iron uptake and release are considered. One involves iron oxidation-reduction sites on the protein. The other allows direct interaction of reagents with the iron-core crystallites. It is concluded that the second model accounts better for the experimental results presented now and in previous publications.

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Ferritin iron uptake and release. Structure-function relationships.

Inhibition by Zn2+ of iron uptake by apoferritin at very low substrate concentrations is shown to be competitive. It is proposed that Zn2+ competes with Fe2+ for sites on the protein at which the oxidation of Fe2+ is catalysed. Interpretation of titration data suggests there are two independent classes of binding site for Zn2+ and several other cations. Sites in one such class are probably on the external surface of the apoferritin molecule. The catalytic binding sites are presumed to be internal and may involve histidine or possibly cysteine as ligands.

The formation of ferritin from apoferritin. Inhibition and metal ion-binding studies

The iron-storage protein ferritin consists of a protein shell and has an iron content of up to 4500 iron atoms as a microcrystalline ferric oxide hydrate. A study was made of the uptake of ferrous iron by apoferritin in the presence of an oxidizing agent at very low iron:protein ratios. At ratios of less than about 150 iron atoms per apoferritin molecule hyperbolic progress curves were obtained, whereas at higher ratios the curves became sigmoidal under the conditions used. A computer model, developed previously (Macara et al., 1972), was shown to account for this result. The experimental evidence indicates that apoferritin binds ferrous iron and catalyses the initial stage in the formation of the ferric oxide hydrate inside the protein shell. This stage involves the oxidation of sufficient iron within the protein molecule to form a stable nucleus on which the growth of the microcrystalline iron-core particles can proceed. A possible schematic mechanism for the action of apoferritin is suggested.

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Terence G. Hoy

Papers

The formation of ferritin from apoferritin. Kinetics and mechanism of iron uptake

On the structure of hemosiderin and its relationship to ferritin.

Ferritin iron uptake and release. Structure-function relationships.

The formation of ferritin from apoferritin. Inhibition and metal ion-binding studies

The formation of ferritin from apoferritin. Catalytic action of apoferritin.