SEQUENCING OF CDNA CLONES THAT ENCODE BOVINE FERRITIN H-CHAIN AND L-CHAIN

The molecular weight of the liver-type subunit (L) of bovine ferritin is much larger than that of the heart-type subunit (H) as determined b y SDS-PAGE (L, 20.5 kDa; H, 18.4 kDa). The migration of these two subu nits on SDS-PAGE gels, relative to each other, is opposite to that rep orted for ferritin L and H subunits in other mammalian species (L, 19 kDa; H, 21 kDa). To determine the cause of this anomaly, full-length c DNA clones of the bovine L and H chains were isolated from a bovine sp leen lambda gt11 cDNA library and sequenced. The amino acid sequences of the L and H chains of bovine ferritin, deduced from their cDNA sequ ences, contained open reading frames coding for 174 and 180 amino acid residues with calculated molecular weights of 19,856 and 20,920 Da, r espectively. The deduced amino acid sequence of the L chain shows 86%, 84%, 87%, 83% and 83% homology with the amino acid sequences of horse , human, rabbit, rat and mouse L chains, respectively. The H chain dis plays a higher homology with the human, rat and mouse H chains (91%, 9 2% and 93%, respectively). In addition, the bovine L chain did not con tain the extra octapeptide present in rodent L chains, and bovine L an d H chains did not react with concanavalin A. The bovine L and H chain s expressed using a baculovirus expression system showed almost the sa me mobilities as those of bovine spleen ferritin, respectively, by SDS -PAGE. These results suggest that the much slower mobility of the bovi ne L chain compared with other mammalian L chains on SDS-PAGE cannot b e attributed to insertion(s) of amino acid(s) or peptide(s) into the L chain, to the deletion(s) of them of it or to the addition of carbohy drate chain(s) but may result from significant differences in the bind ing affinity of SDS for bovine ferritin L chains. (C) 1997 Elsevier Sc ience Inc.