HUMAN FERRITIN H-CHAINS CAN BE OBTAINED IN NONASSEMBLED STABLE FORMS WHICH HAVE FERROXIDASE ACTIVITY

We found conditions to obtain the Leu-169 --> Arg mutant of human ferr itin H chain in a stable and non-assembled state. The protein obtained is an oligomer of subunits with a high degree of structured conformat ion, and when concentrated it re-assembles into ferritin cages. Functi onal studies showed that (i) it promotes iron oxidation like the assem bled ferritin, but at slower rate, (ii) it is readily precipitated by the oxidised iron unless apotransferrin or L-chain ferritin are added to sequester Fe(III). The results confirm that ferroxidase activity is located within the H-chain, and indicate that the cages of the fully assembled ferritins are important not only in maintaining iron in a so luble form, but also in eliciting the activity of the ferroxidase cent res.