Phosphorylation by cell surface protein kinase of bovine and human fibrinogen and fibrin.

Human and bovine fibrinogen as well as fibrin are shown to be phosphorylated by Co631 (monolayer, hamster) and RPL12 (suspension, chicken) cells by their surface protein kinase of the casein kinase II type. The phosphate label is introduced into the alpha-peptide. The kinase system phosphorylates serine residues and utilizes GTP equally well as ATP. The participation of intact cell surfaces indicates the possibility of phosphorylation of extracellular fibrinogen independently of the site of its biosynthesis.