Abstract
The in vitro binding of manganese to serum proteins in cattle was investigated using sera exhibiting the following transferrin pheno-types: Tf AE, Tf AA, Tf DD and Tf EE. After the addition of Mn(54) to serum and dialysis, where excess of manganese was removed, it was found by means of starch gel electrophoresis that the radioactivity was confined to the electrophoretically different transferrin fractions. Variations in the amounts of radioactivity bound in the individual sera suggested fluctuations in the manganese-binding capacity of cattle sera.