Globin-methionine complexes formed during labelling studies

In implementing globin synthetic measurements using our recently described technique of Cellogel separation of 35S-methionine-labelled globin chain we sometimes encountered aberrant results. We discovered the presence of prominent radioactive bands trailing both the alpha and beta globin chains. Such bands were not present when 3H-leucine served as a label. These bands were not due to contaminants in the 35S-methionine. Their formation could be prevented by including in the incubating mixture 1 mM cystine, cysteine or homocysteine. The bands could not be removed by trichloracetic acid or acid acetone precipitation but did disappear almost entirely after prolonged dialysis against a urea-containing buffer. The trailing bands appear to represent the result of the firm, but not covalent, binding of methionine to globin during the protein synthetic process. Since methionine is commonly used as a label for newly synthesized protein, this phenomenon may be important not only in the investigation of globin synthesis, but also in the study of the synthesis of other proteins.