Isolation and characterization of ferritin from the liver of the rainbow trout (Salmo gairdneri R.).

A method for the purification of ferritin from rainbow trout liver by heat extraction and gel filtration is described. The number of iron atoms varied from 500 to 2000 in purified ferritin. The neutral sugar composition detected was 86 mol of glucose, 24 mol of fucose, 12 mol of galactose, and 8 mol of mannose per mol of ferritin and apoferritin. Release of iron was achieved using low molecular weight chelating agents. The order of effectiveness of chelators was nitrilotriacetate greater than EDTA greater than citrate. Removal of the iron does not imply reduction of Fe3+. The rate of release of iron increased with decreasing pH. The slowest release was at pH 7.5. The endogenous chelator is not only sulphydrylic but seems to include carbohydrates that participate in the binding of Fe2+. Trout ferritin exhibits heterogeneity upon isoelectric focusing; four isoferritins with pI values of 4.5 to 4.85 were detected. This heterogeneity represents polymorphic, not polymer, forms. The amino acid composition differs from that of ferritins from other species. High concentrations of glutamic and aspartic acids, alanine, leucine, glycine, and lysine were detected along with low concentrations of methionine and cysteine.