Polymer and Materials
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Human fibrinogen was treated with thrombin in the presence of fibrinoligase (Factor XIIIa) and calcium ion at pH 8.5, ionic strength 0.45, and the ensuing polymerization was interrupted at various time intervals (t) both before and after the clotting time (tc) by solubilization with a solution of sodium dodecylsulfate and urea. Aliquots of the solubilized protein were subjected to gel electrophoresis on polyacrylamide gels after disulfide reduction by dithiothreitol and on agarose gels without reduction. The degree of γ-γ ligation was determined from the former and the size distribution of ligated oligomers, for degree of polymerization x from 1 to 10, from the latter. In some experiments, thrombin was inhibited, after partial polymerization, by p-nitrophenyl-p′-guanidinobenzoate. From these, it was concluded that for thrombin concentration ≤0.013 units/mL and fibrinoligase ≥30 mg/L, oligomer assembly is rapid compared with peptide A release and ligation is rapid compared with assembly. Under these conditions, the theory of the first paper of this series describes rather well the time dependences of the degree of γ-γ ligation, the weight fractions of monomer and small oligomers, and the number- and weight-average degrees of polymerization after solubilization of the staggered overlapped assemblies, each of which splits to give two strands of end-to-end ligated oligomers. The theory assumes that the second A peptide is released by thrombin more rapidly than the first by a factor q, which, from the experimental data, is determined to be 16. The subsequent assembly into staggered overlapped oligomers follows the statistics of linear polycondesation taking into account the presence of both difunctional and monofunctional combining units. For higher thrombin or lower fibrinoligase concentrations, ligation fails to keep pace with oligomer assembly, and the size distributions after solubilization show a higher proportion of very small and a lower proportion of larger ligated oligomers, owing to separation of the staggered overlapped assemblies into smaller fragments.
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