Ferritin in the Fungus Phycomyces

Citation

David, Charles Newbold (1968) Ferritin in the Fungus Phycomyces. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/NNQ9-TM81. https://resolver.caltech.edu/CaltechETD:etd-10032002-103720

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The iron storage protein ferritin has been purified from mycelium, sporangiophores, and spores of the fungus Phycomyces blakesleeanus. Its morphology in the electron microscope and the electron diffraction pattern of its iron core are almost indistinguishable from those of horse ferritin. Its protein/iron ratio is 4.7. It has a sedimentation coefficient of 55S and a buoyant density in CsCl density gradients of 1.82 g/[cubic]cm. In the cytoplasm of Phycomyces, ferritin is located on the surface of lipid droplets (0.5-2.0[micron] diameter) where it forms crystalline monolayers which are conspicuous in electron micrographs of sporangiophore thin sections. The ferritin-lipid complex can be isolated from sporangiophore lysates. Treatment of the complex with detergent separates ferritin from the lipid. The level of ferritin iron in Phycomyces is regulated by the iron level in the growth medium. A 20-40 fold increase in ferritin has been achieved by supplementing the medium with iron. Ferritin and iron are concentrated in spores. In lysates of sporangiophores grown on low-iron growth medium about 80% of the iron is recoverable in the spores. At least one half of this spore iron can be extracted and is shown to be ferritin. The remaining iron is unextractable. There is no extractable low molecular weight iron in ungerminated spores. When ferritin is present in "limiting" amounts in spores, it disappears rapidly upon germination and simultaneously a low molecular weight form of iron becomes extractable. When present in large amounts in spores, ferritin does not disappear following germination although low molecular weight iron does become extractable. These results suggest that ferritin in Phycomyces spores functions as a source of iron in the early stages of germination. Because the initial intracellular ferritin concentration and the external iron concentration of the germination medium can be varied, Phycomyces spores are potentially a very useful system in which to study the mechanism and control of ferritin iron metabolism.

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