In vitro stimulation of apoferritin synthesis by iron

The apparent induction of apoferritin synthesis by iron has been examined in cell-free systems from rat and rabbit liver. Both systems allowed the complete synthesis de novo of apoferritin isolated by chromatographic or immunological means. Addition of iron at levels of 0.2--1 mM specifically stimulated incorporation of radioactive amino acids into apoferritin purified after classical heat extraction. The effect was also observed when iron was added at the end of the incubation period in the absence of continuing protein synthesis. Further, iron addition had no effect on the amount of newly synthesised apoferritin subunits as estimated by direct immunological precipitation from the reaction mixture. These results suggest that iron acts at some stage subsequent to translation in stimulating apoferritin biosynthesis.