NOVEL PROPERTIES OF L-TYPE POLYPEPTIDE SUBUNITS IN MOUSE FERRITIN MOLECULES

Properties of the L- and H-type polypeptide subunits forming ferritin 24-mer molecules in mice were investigated, using the products of in v itro transcription and translation from the two cloned genes, and reco mbinant ferritin molecules (H(24)L(0) or H(0)L(24) produced by transfo rmation in Escherichia coil, Several different conditions for analytic al electrophoresis reproducibly show that the relative migration posit ion of the two mouse ferritin subunits is reversed from that reported for ferritin H- and L-subunits in all other mammals; since mouse and h uman H-polypeptides almost co-migrate, this unusual relative mobility is due largely to novel properties of the murine L-subunit. This unusu al electrophoretic property of the mouse L-subunit has led to conflict ing reports about the subunit composition of natural mouse ferritin. H ere, we show that the single major electrophoretic band given by liver ferritin purified from mice having a short-term iron overload matches that produced by the genetically defined L-polypeptide and that some bona fide H-subunits are also detected. In conclusion, it is reasonabl e to assume that, when mouse ferritin samples will be analyzed under t he same conditions as those described here, the slower species will co rrespond to the L-type subunit. However, when dealing with ferritin fr om species other than human or mouse, it should be kept in mind that u pon electrophoretic analysis of ferritin polypeptide, the designation of an electrophoretic band as being H or L-type subunits will be very uncertain without corroboration hom genetic, immunological, or amino a cid sequencing data.