Labelled Fibrinopeptide B and the Denaturation of Fibrinogen on Over-iodination

Abstract

ACCORDING to McFarlane¹, rabbit fibrinogen labelled with more than 0.5–0.6 atoms of iodine per molecule of protein behaves in vivo in a manner noticeably different from that of preparations iodinated at lower mean substitution levels. In the former case, intravascular protein-bound radioactivities decreased more rapidly during the first 24–36 h after injection and, at the same time, labelled breakdown products in the plasma reached abnormally high concentrations. These signs of denaturation, however, were missing if the labelled protein was allowed to circulate for a day or more in an intermediate host, suggesting that over-iodinated fibrinogen molecules had been “screened” out. Other investigators² confirmed McFar-lane's observations and, using Oncley's statistical results³, it appears that fibrinogen molecules carrying more than two atoms of iodine are recognized by the body as different from the native protein⁴.