Phosphorylation of hepatic insulin receptor by casein kinase 2.

Casein kinase 2 was able to phosphorylate the beta-subunit of hepatic insulin receptor in the presence of either ATP or GTP. Phosphorylation by casein kinase 2 was observed even in the absence of insulin, was inhibited by low heparin concentrations, and led to the incorporation of phosphate on serine and threonine residues. Casein kinase 2 phosphorylation of insulin receptor partially decreased its tyrosine kinase activity.