Heterogeneity in horse ferritins. A comparative study of surface charge, iron content and kinetics of iron uptake

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Abstract
Horse ferritins from different organs show heterogeneity on electrofocusing in Ampholine gradients. Both ferritin and apoferritin from liver and spleen could be fractionated with respect to surface charge by serial precipitation with (NH4)2SO4. In the ferritin fractions, increasing Fe content parallels increasing isoelectric point. After removal of their Fe, those fractions which originally contained most Fe accumulated added Fe at the fastest rates. When unfractionated ferritins from different organs were compared the average isoelectric point increased in order spleen < liver < kidney < heart. The order of initial rates of Fe uptake by the apoferritins was spleen > kidney > heart and initial average Fe contents also followed this order. The relatively low rates of Fe accumulation by Fe-poor molecules may have been due to structural alteration, to degradation, to activation of the Fe-rich molecules or to other factors.