Molecular weight of human fibrinogen derived from phosphorus determinations.

1. Fibrin clots obtained from diluted human plasma with bovine thrombin often contain amounts of phospholipids that cannot be diminished by further plasma dilution. 2. The ;cold insoluble residue' obtained during fibrinogen preparation has a higher phosphorus content than the purified fibrinogen. 3. Evidence showed that adsorption of phospholipids or phosphorus-containing fibrinopeptides on purified fibrinogen or fibrin was unlikely. 4. O-Phosphorylserine was detected in acid hydrolysates of human fibrin. 5. On the basis of phosphorus determinations the average molecular weight of human fibrinogen cannot be less than 342000 (304000-383000) for a group of ten donors, and 265000 for two other persons, assuming 1 phosphorus atom/molecule and incomplete splitting of the phosphorus-containing fibrinopeptide. Complete splitting of the phosphopeptide would require molecular weights twice as high. 6. Fibrinolysis was a possible cause of lower phosphorus contents found in isolated fibrinogen and fibrin from a donor who showed apprehension during blood collection and in a fibrinogen preparation that had been submitted to prolonged dialysis.