Partial Chemical Characterization of Rat Fibrinogen*

Rat fibrinogen has been purified and compared with bovine and human fibrinogen with respect to a number of chemical characteristics, including molecular size, charge distribution, NH,-terminal amino acids, total amino acid composition, and interspecies immunological cross-reactivity. Although human and bovine fibrinogen demonstrated three nonidentical polypeptide chains by sodium dodecyl sulfate gel separations and by CM-cellulose separations, rat fibrinogen Acu and B/l chains exhibited identical molecular weight sizes as well as identical charges. The presence of two nonidentical chains in these preparations was shown by qualitative NH,-terminal sequence analyses. The y chain of rat fibrinogen was also shown to be quite distinct from the y chains of human and bovine fibrinogen in its elevated content of cysteinyl and methionyl residues. Rat fibrinogen possesses the first reported blocked y chain NH,-terminal amino acid of any species. It is concluded that, although many chemical properties of rat fibrinogen are unique, the basic molecular structure has remained consistent when compared with that of fibrinogen from the vertebrates studied thus far. Moreover, the inducibility of this system, together with the partial chemical characterization of the fibrinogen molecule, provides important information for the use of rat fibrinogen as a model system in studying the biosynthesis and assembly of this complex molecule.