Amphibian Red Blood Cell Ferritin

Abstract

Erythroid ferritin was isolated from tadpole red blood cells, an unusually abundant source, with an iron content of 12%. The apoprotein was characterized by sedimentation equilibrium studies, sodium dodecyl sulfate gel electrophoresis, and by determination of amino acid composition. Tadpole red cell apoferritin has a molecular weight of 478,000, a subunit size of 19,600, and an amino acid composition similar to that of horse spleen apoferritin, particularly in its proline content. However, there is little or no cysteine in the tadpole protein in contrast to that from horse spleen; two other tadpole red cell proteins also have little or no cysteine. The amount of ferritin in amphibian red blood cells decreased from 0.9% of the soluble protein in the tadpole to 0.08% in the frog as measured immunologically; ferritin could not be detected in lysates of frog cells using gel electrophoresis. A large non-hemoglobin iron pool in the tadpole red cell was indicated not only by the amount of ferritin but also by the observation that cell suspensions could incorporate 14C-amino acids into hemoglobin without incorporating 59Fe into hemoglobin. Red cell suspensions from adult frogs incorporated 14C-amino acids and 59Fe into hemoglobin.