CALCIUM-INDUCED FORMATION OF FIBRINOGEN -- FIBRIN COMPLEXES
Presence of calcium chloride (8.3 mM) at u = 0.1 enhanced precipitate formation in several different fibrinogen preparations. The precipitate had gel like properties and demonstrated syneresls when disturbed. Precipitation proceeded in the time dependent manner with a plateau after 30 min. The amount of precipitate ranged from 4-24% of total protein content of different preparations. Precipitates did form at u = 0.1 without calcium ion; however, the amount of protein was 3 to 7 fold less than
... 7 fold less than when calcium ion was present.SOS gel electrophoresis of calcium precipitates demonstrated cross-linking of gamma chains. Cross-linking, but not precipitate formation was blocked by parachloromercurie-benzoate (PCMB). The precipitates were redissolved in 2M urea, treated with thrombin, and analyzed for flbrinopeptide content by HLPC. Precipitate formed in absence of calcium ion contained 19% of FPA and 89% of FPB. Precipitates formed in the presence of calcium ion contained 49% of the expected amount of FPA and 98% of expected FPB. The precipitation phenomenon could be reproduced after fibrin monomer-free fibrinogen (prepared by dialysis of calcium supernatants against calcium free buffer) was treated briefly with thrombin.The above finding suggests that calcium ion enhances polymerization of Intact fibrinogen and molecules missing one or two FPA's.