Bovine fibrinogens: Reversible polymer formation |
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Authors: | Carter M Becker David F Waugh |
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Institution: | Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 USA |
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Abstract: | Reversible flbrinogen polymer formation was examined at pH 6.6 and Γ/2 0.3. The equilibrium fraction of fibrinogen present as polymer, (Pmf)e, was determined by gel filtration for fibrinogen concentrations, FO, from 48 to 166 μm. Using FO in molarity, the experimental relation is ln FO(Pmf)e] = 3.53 lnFO(1 ? (Pmf)e)] + 23.73. This relation and attendant confidence limits are examined assuming, during filtration, that the original polymer population is either stable or selected polymer species dissociate to monomer. The possibility that all polymers are open is excluded since the calculated microscopic association constant would then increase with FO. Acceptable models are based on the assumptions that polymers are open, with association constant Ka, until restricted by closure, with association constant Kr, at an integral degree of polymerization, n. Values are selected on the basis that interaction parameters are independent of FO and that the required molar decrease in free energy is a minimum. Assuming polymer stability, the experimental relation at 273 °K gives = 736 m?1. Temperature dependence gives = ?48.8 e.u. indicates a relation between changes in entropy. The probability is >0.90 that , which indicates a greater loss of degrees of freedom on closure than on association. Conclusions are not altered by the assumption that only the closed polymer species is stable. As ionic strength is decreased at pH 6.6, Ka increases. The clotting time of an otherwise constant system decreases as system Pmf is increased. |
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Keywords: | To whom correspondence should be addressed |
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