A membrane-bound protein kinase from mouse liver stimulated by iron

At microM levels, iron stimulates strongly the in vitro phosphorylation of a membrane protein from mouse liver. This phosphorylation also occurs in the absence of other added divalent cations but to a lower degree. In SDS gels the phosphorylated protein has app. Mr 250 000 in the absence of mercaptoethanol and Mr 130 000 in its presence. It is phosphorylated on threonine residues.