Electron microscopic studies of human haemosiderin and ferritin.

Abstract

SUMMARY Ferritin and haemosiderin were isolated from fresh frozen human spleens that had been removed from patients with secondary iron overload due to multiple transfusions. Haemosiderin was solubilised by a novel technique that maintains its integrity. Unstained preparations of haemosiderin and ferritin were visualised and quantitative measurements made of the volumes of iron core. The mean diameter of the ferritin core (6.4 nm) was larger than that of haemosiderin (5-7 nm). In addition, haemosiderin, in contrast to ferritin, showed a large number of cores of less than 5 nm in diameter. Negatively stained preparations of haemosiderin and ferritin were visualised, confirming the small core size of the haemosiderin. The protein shell of haemosiderin, unlike that of ferritin, was thinner and irregular. These findings are consistent with the suggestion that haemosiderin is derived from ferritin by partial proteolysis and partial solubilisation of the iron core, presumably by lysosomal action.

Electron nanodiffraction and high-resolution electron microscopy studies of the structure and composition of physiological and pathological ferritin

“…The hemosiderin cores present in human liver of PH patients are formed by a mixture of two phases: a minor ferrihydrite phase (about 20%) and a major, poorly crystallized phase Mann et al, 1988) with reticular distances at 0.249, 0.212, and 0.153 nm very near to d 111 (0.248 nm), d 200 (0.215 nm), and d 220 (0.152 nm) of the fcc structure with a ¼ 0:43 nm. The hemosiderin shell is thinner than the ferritin shell, irregular and often incomplete (Weir et al, 1984b(Weir et al, , 1985. Analysis of peptides present in hemosiderin molecules shows bands between 12.9 and 17.8 kDa significantly smaller than ferritin (20 kDa) (Ward et al, 1994;Weir et al, 1984b).…”

Ferritin and ferritin isoforms I: Structure–function relationships, synthesis, degradation and secretion

“…However, not all ferritin molecules in these lysosomal organelles are susceptible to the action of lysosomal proteases. Degradation of the ferritin protein shell results in the exposure of the iron oxyhydroxide mineral cores followed by aggregation of these oxyhydroxide particles and the formation of insoluble masses of iron oxyhydroxide (haemosiderin) (Fischbach et al, 1971;Richter, 1978;Weir et al, 1985). Although the main purpose of the formation of haemosiderin would appear to be protection against iron overload, these larger masses of ferritin/ haemosiderin can, at a much slower rate, also release iron.…”

Genetically encoded iron‐associated proteins as MRI reporters for molecular and cellular imaging

“…At high iron loading, ferritin aggregates in the lysosomes to form hemosiderin . Hemosiderin is a mixture of ferritin, lipids, and iron that is often formed during pathological processes and neurodegenerative diseases associated with altered brain iron metabolism such as Alzheimer's and Parkinson's diseases, and multiple sclerosis .…”