Structural analysis of haemin demetallation by L-chain apoferritins

► Cofactor from horse spleen apoferritin and from recombinant mutant apoferritin is a N-ethylprotoporphyrin IX. ► Mass spectrometry and X-Ray crystallographic studies identified this cofactor as a N-ethylprotoporphyrin IX. ► L chain ferritins are capable of binding and demetallating haemin in vivo and in vitro.