On ferritin heterogeneity. Further evidence for heteropolymers.

Tissue ferritins from the horse, rat, and human consist of multiple isoferritins some of which are common to more than one tissue in the same individual. Subunit analyses indicate that the ferritins from all three species are similarly composed of only two types of subunit with an approximate Mr of 21,000 and 19,000, designated H and L. The relative amounts of these subunits vary progressively throughout the isoferritin spectrum. Amino acid analyses and tryptic peptide maps indicate that the H and L subunits have extensive sequence homologies and that both are species-specific. Both subunits have been identified as the primary products of apoferritin synthesis in a wheat germ lysate programmed by rat liver mRNA. These results substantiate our proposal (Adelman, T. G., Arosio, P., and Drysdale, J. W. (1975) Biochem. Biophys. Res. Commun. 63, 1056-1062) that tissue ferritins are not unique homopolymers but families of hybrid molecules consisting of different proportions of two subunit types.