Cation dependence of the phosphorylation of specific residues in red cell membrane protein band 3.

Phosphorylation of anion channel protein (ACP), the major component of erythrocyte protein band 3, was achieved in red cell ghosts in buffers containing vanadate (an inhibitor of phosphatases) and Mg2+ or Mn2+, known specific activators of the various kinases present in the red cell membrane. The anion channel protein was isolated to purity and the phosphorylated aminoacids were determined. The present results show that the phosphorylation of anion channel protein in its membraneous environment leads to an equal phosphorylation of tyrosine and serine plus threonine in the presence of Mg2+. In contrast, phosphotyrosine represents 80% of the total when Mn2+ is the activator.