Molecular weight of bovine fibrinogen by sedimentation equilibrium

Abstract

This work was undertaken primarily to evaluate a recent report, based on light-scattering measurements, that the previously accepted molecular weight of bovine fibrinogen is valid at 20 °, but that the molecule is dissociated into two subunits of equal weight by EDTA or by raising the temperature to the physiological one (37 °). In the present work, molecular weights were measured by sedimentation equilibrium, using the meniscus depletion method. Preparations of bovine fibrinogen from fresh blood and from commercial plasma fraction I were investigated. At both 20 and 37 °, and with both preparations, the observed molecular weights agreed with the generally accepted value (3.3–3.4 × 10 5), and there was no effect of EDTA at 20 °. Sedimentation velocity experiments at both temperatures gave nearly identical sedimentation coefficients when calculated for standard conditions. The presence of EDTA caused a small decrease in the standard sedimentation coefficient, probably because of an expansion of the molecule. The present results give the molecular weight of bovine fibrinogen as (3.36 ± 0.04) × 10 5, with no indication of dissociation at 37 ° or in the presence of EDTA.