“…We have shown (Macara et al, 1972(Macara et al, , 1973, as have others (Niederer, 1970;Bryce & Crichton, 1973b), that horse spleen apoferritin catalyses the oxidation of Fe(II) to Fe(III), retaining the latter as hydrous ferric oxide to give ferritin. We wished to discover whether individual 'isoferritins' (ferritins from different tissues or fractions of different isoelectric point from the same tissue) showed any functional differences as judged by their ability to oxidize and accumulate iron in vitro and to observe the effects of both removal and addi-tion of iron on their focusing patterns.…”