PubMed · 4088343
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H G van Eijk, C van der Heul. 1985-12-14. [Iron-binding proteins].. https://pubmed.ncbi.nlm.nih.gov/4088343/
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Iron release from the iron storage protein ferritin has been studied extensively because of its important role in oxidative stress and its possible role in the progression of Parkinson's disease. For many years external indicators, notably strong iron(II) chelators, have been used to investigate this reaction. Such chelators can, however, drastically affect the electrochemical and thermodynamic properties of iron. The present study is unique in that it has been possible to follow a reaction taking place within the ferritin shell. This was made possible by our serendipitous discovery that, at physiological pHs, the oxidation product of 6-hydroxydopamine (a deprotonated quinone) acts as its own indicator (G. N. L. Jameson and W. Linert, J. Chem. Soc., Perkin Trans. 2, 2001, 563-568). The redox equilibrium data and the kinetics of the formation of this red-coloured species can only be explained on the basis that reduction of the iron(III) takes place within the ferritin shell. This is, in fact, the first time that a reaction actually taking place inside the ferritin shell has been followed. It has also been established that, at least in vitro, all eight hydrophilic channels are capable of being simultaneously involved in the reaction. It has also been possible to calculate the rate of oxidation of the 6-hydroxydopamine within the ferritin and it is demonstrated that a redox equilibrium is established within the protein. Finally, evidence is provided confirming that chelators are in fact intrinsically linked to iron removal from ferritin.
Iron is a metal required by most microorganisms and is prominently used in the transfer of electrons during metabolism. The gathering of iron is, then, an essential process and its fulfillment becomes a crucial pathogenetic event for zoopathogenic fungi. Iron is rather unavailable because it occurs on the earth's surface in its insoluble ferric form in oxides and hydroxides. In the infected host iron is bound to proteins such as transferrin and ferritin. Solubilization of ferric iron is the major problem confronting microorganisms. This process is achieved by two major mechanisms: ferric reduction and siderophore utilization. Ferric reductase is frequently accompanied by a copper oxidase transport system. There is one example of direct ferric iron transport apparently without prior reduction. Ferric reduction may also be accomplished by low molecular mass compounds. Some fungi have evolved a process of iron acquisition involving the synthesis of iron-gathering compounds called siderophores. Even those fungi that do not synthesize siderophores have developed permeases for transport of such compounds formed by other organisms. Fungi can also reductively release iron from siderophores and transport the ferrous iron often by the copper oxidase transport system. There is a great diversity of iron-gathering mechanisms expressed by pathogenic fungi and such diversity may be found even in a single species.
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