{'fraction_non_alphanumeric': 0.018726591760299626, 'fraction_numerical': 0.018726591760299626, 'mean_word_length': 4.862068965517241, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Metabolic and chemical features of ferritins, a series of iron-inducible tissue proteins.

FERRITIN is an iron storage protein which has been observed in a wide range of phyla from fungi 1 through the plant2 and animal kingdoms. The ferritin molecule retains a characteristic structural pattern of protein subunits forming a shell surrounding a core of heterogeneous iron oxyhydroxide micelles with some phosphate. 3 The iron core can be removed chemically without destroying the protein shell (apoferritin). Apoferritin has a molecular weight of about 440,000 and is thought to consist of 20 4 or 245 subunits that may be identical, each of about 20,000 molecular weight. The iron content of holoferritin is variable and maximally attains 5000 atoms Fe per molecule,6 so that the weight of iron can represent an addition of 35% to the weight of the protein shell. The other major iron-rich tissue component, hemosiderin, is much less well-defined chemically, but is recognized by its insolubility and variable protein content. The latter is less than that of ferritin, so that the proportion of iron to protein is much larger.7-9 It is possible that hemosiderin is a degradation product of ferritin. Ferritin and hemosiderin are the principal components of nonheme iron present in mammalian tissues, and they account for about 15% of the total amount of iron in the body.10 Under normal conditions ferritin is probably the main storage site for iron in the body. It is present in highest concentration in liver, spleen and bone marrow,10 but has been identified in all tissues examined and must be regarded as an essential feature of the iron metabolism of all cells which ensures available iron without the attendant toxicity of free iron. Thus, tumor cells retain their capacity for ferritin synthesis, as will be demonstrated in a subsequent section of this review.