Bovine fibrinogen modified with 3H-acetic anhydride (3H-AcOAc)

The method is described for acetylation of bovine fibrinogen with 3H acetic anhydride (3H-AcOAc). Preparations acetylated at pH 7.8 with 10 to 40 molar excess of 3H-AcOAc were found to contain 8 to 13 moles of acetyl residues per mole of fibrinogen. The content of clottable protein and ultraviolet (UV) spectra were unchanged as compared with control unlabeled preparations. The rate of clotting with thrombin was only slightly affected. The investigations on distribution of 3H-acetyl groups in products of proteolysis of acetylated fibrinogen by thrombin demonstrated a preferential acetylation of fibrinopetide A and absence of radioactive tracer in fibrinopeptide B. Incorporation of the label into fibrinopeptide A opens the possibility for application of fibrinogen labeled with 3H-AcOAc as a convenient substrate for selective investigation on the enzymatic phase of clotting.