Investigation of the aggregation and activation of prothrombin using quasi-elastic light scattering

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Abstract
The technique of quasi-elastic light scattering was used to measure the translational diffusion coefficient, D, of purified human prothrombin in buffered aqueous solutions and to monitor for the 1st time the fragmentation of this protein as it is converted to thrombin. The values of D20,w, [value of D at 20.degree. C in water] measured at 2 different concentrations, are 4.72 .times. 10-7 cm2/s at 2 mg/cm3 and 4.51 .times. 10-7 cm2/s at 5 mg/cm3; the corresponding MW (of 92,000 and 120,000), obtained by combining sedimentation velocity measurements with the diffusion data, confirm the presence of molecular aggregates of prothrombin in these solutions. These results, as well as analysis of the intensity-intensity autocorrelation functions from 2-component systems with various dimer conformations, indicate the presence of end-to-end dimers in these prothrombin solutions. The values obtained for D indicate a dimer weight fraction of 0.4-0.5 in the 2 mg/cm3 solution and 0.6 or greater in the 5 mg/cm3 solution. The fragmentation of prothrombin was monitored in a nonphysiologic activation system, containing taipan snake venom, dihexanoylphosphatidylcholine and CaCl2. At a temperature of 15.degree. C, conversion to thrombin proceeded very slowly and was still incomplete after 90 h. A method for determining the percentage of converted prothrombin is an activated system containing aggregates from the average value of D and light scattering data is discussed.

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