ISOLATION AND CHARACTERIZATION OF CLOTTABLE LOW MOLECULAR WEIGHT FIBRINOGEN DERIVED BY LIMITED PLASMIN HYDROLYSIS OF HUMAN FRACTION I-4

As part of an investigation into the origin of a naturally occurring high ethanol solubility, low molecular weight, human fibrinogen (fraction 1-8), low solubility, high molecular weight, fibrinogen (fraction 1-4) was subjected to limited plasmin degradation. Early in this hydrolysis, a high ethanol solubility derivative was formed, which was then purified to ≤95% clottability (I-8D5). Fractions I-4, I-8, and I-8D5 were compared. Molecular weights were 347,000 for I-4, 273,000 for 1-8, and 262,000 for I-8D5. Fractions I-8 and I-8D5 had the same sialic acid and hexose contents (w/w) and both values were significantly greater than those of 1-4. The N-terminal amino acids were qualitatively and quantitatively the same (mole/mole) for all three fractions. All three preparations exhibited heterogeneity when subjected to DEAE gradient chromatography. Tyrosine :tryptophan ratios did not differ significantly between the three fractions. Fractions 1-8 and I-8D5 displayed retarded polymerization of fibrin monomer which resulted in both having longer thrombin times than 1-4. When compared with previously described products of in vitro fibrinogenolysis, I-8D5 was considered to be representative of the earliest detectable stage of fibrinogenolysis. The delayed clotting of I-8D5 was considered to be due to slowed polymerization rather than inhibition relating to the thrombin susceptible site. Further conclusions from the data were that the early plasmin-induced cleavages were from the C-terminal end of the molecule, releasing peptides, and little, if any, carbohydrate, without impairing ultimate clottability. The close resemblance between I-8D5 and 1-8 in these studies supported the concept that 1-8 is an in vivo proteolytic product derived from a higher molecular weight fibrinogen, such as fraction 1-4. © 1969, American Chemical Society. All rights reserved.