SPECIFIC PROTEIN-PHOSPHORYLATION INDUCED BY FIBRINOGEN IN RAT PERITONEAL-MACROPHAGES

Fibrinogen is a plasma glycoprotein involved in the formation of blood clots, leukocyte adhesion and phagocytosis. In this study one of the early cellular events induced by fibrinogen-receptor binding was shown to be a highly specific phosphorylation of 85 kDa protein, Two to fou r-fold increases of phosphorylation of 85 kDa protein was observed in both a time- and dose-dependent manner, The phosphorylation of the 85 kDa protein was detected within 10 min, following ligand binding and r eached a maximum level after 30 min, The phosphorylation of the 85 kDa protein was stimulated by fibrinogen, not by 12-0-tetradecanoyl phorb ol-W-acetate, Phosphoamino acid analysis of the 85 kDa protein showed that the serine residues were amino acids receiving the phosphates fro m ATP by action of protein kinase induced by fibrinogen-receptor bindi ng, The data revealed that fibrinogen-receptor binding initiates a cha in of events including serine-protein kinase activation and specific p rotein phosphorylation as parts of the intracellular events leading to cell adhesion and phagocytosis.