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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Proteins are selectively sequestered by a number of cell types. However, only in oocytes is the process sufficiently aggravated and specific to be readily studied. In these cells certain serum proteins are taken up in proportions different from those found in the serum. In vitro incubations of hormonally stimulated and synchronous mosquito oocytes show that the only protein capable of initiating the transport process is the female specific yolk protein. Heterologous proteins such as IgG, bovine serum albumin, cytochrome C, and ferritin are inactive. The female specific protein is a phosphoglycolipoprotein. It is synthesized in the fat body, a liver analog in the insect, and passed into the serum before being transported into the oocytes. Preliminary kinetic analysis shows the uptake process to be specific with an apparent Km of about 10(-7) M. Glycolytic inhibitors stop protein uptake. The receptor-mediated binding steps in the transport process are most easily studied in the chicken because of the enormous amount of oocyte membrane available from a given oocyte and because up to 1 gm of protein is normally transported per day per oocyte. IgG and the hen specific phosvitin lipovitellin are two of the physiologically important proteins that are transported intact into the chicken oocytes. The uptake appears selective as shown by studies with iodinated proteins. Ferritin conjugated to IgG is shown by electron microscopy to bind to isolated plasma membranes only where coated pits have formed, whereas ferritin alone is not seen localized on any membrane surface. These very specialized regions of the membrane are similar to micropinocytotic pits but, in addition, possess on their cytoplasmic side dense ridges that form the coat. Transport involves binding to the coated pits, the pinching off of the pits, and the subsequent movement of the coated vesicles in the cytoplasm.
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PMID:Protein transport: a selective membrane mechanism. 93 39

The endocytosis of cationized ferritin and of a phosvitinferritin conjugate by cells of the chick embryo area pellucida has been examined. Cationized ferritin was bound mainly to the free surface of the epiblast but was absent from the region of the primitive streak. The binding was patchy and experiments suggest that the anionic sites which bind cationized ferritin are themselves naturally clustered. Uptake of cationized ferritin was exclusively by coated pits. The resulting coated vesicles delivered the cationized ferritin to membrane-bound sites of accumulation in the cytoplasm and to the close vicinity of Golgi bodies. The cationized ferritin was frequently found to share intracellular vacuoles with yolk granules. The uptake was not affected by the presence of microfilament or microtubule-inhibiting agents. Native ferritin, even at concentrations forty times that of cationized ferritin, was not bound or endocytosed. Coated pits in the epiblast were often associated with overlying extracellular yolk granules. This suggested that the yolk might be inducing the formation of the coated pits. The yolk protein phosvitin was coupled to ferritin and this conjugate was found to be endocytosed by coated pits. This uptake was inhibited in the presence of an excess of free phosvitin but not by albumin, indicating some selectivity for phosvitin over other proteins. The phosvitin conjugate was also found sharing intracellular vacuoles with yolk. We conclude that the cells of the area pellucida, and in particular those of the epiblast, have an active coated vesicle uptake system which may be able to selectively endocytose yolk or yolk protein.
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PMID:Cationized ferritin and phosvitin uptake by coated vesicles of the early chick embryo. 619 97

Phosvitin, a phosphoprotein known as an iron-carrier in egg yolk, binds almost all the yolk iron. In this study, we investigated the effect of phosvitin on Fe(II)-catalyzed hydroxyl radical ((.-)OH) formation from H(2)O(2) in the Fenton reaction system. Using electron spin resonance (ESR) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and deoxyribose degradation assays, we observed by both assays that phosvitin more effectively inhibited (.-)OH formation than iron-binding proteins such as ferritin and transferrin. The effectiveness of phosvitin was related to the iron concentration, indicating that phosvitin acts as an antioxidant by chelating iron ions. Phosvitin accelerates Fe(II) autoxidation and thus decreases the availability of Fe(II) for participation in the (.-)OH-generating Fenton reaction. Furthermore, using the plasmid DNA strand breakage assay, phosvitin protected DNA against oxidative damage induced by Fe(II) and H(2)O(2). These results provide insight into the mechanism of protection of the developing embryo against iron-dependent oxidative damage in ovo.
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PMID:Egg yolk phosvitin inhibits hydroxyl radical formation from the fenton reaction. 1521 98