INCORPORATION AND RELEASE OF INORGANIC-PHOSPHATE IN HORSE SPLEEN FERRITIN

When ferritin is reconstituted from Fe and apoferritin in vitro in the presence of P(i), the product obtained differs both from native ferritin and from ferritin reconstituted in the absence of P(i). When the latter is incubated with P(i) the product resembles native ferritin with respect both to the pattern of P(i) incorporated per molecule or per Fe atom and to the ease of release of this P(i) relative to Fe release. It is concluded that much of the P(i) of native ferritin is adsorbed on surfaces of ferritin iron-core crystallites. The results also suggest that P(i) is not present at the intracellular site of Fe incorporation into ferritin, but is added after Fe.