Fibrinogen: agreement of experimental and calculated hydrodynamic data with electron-microscopic models

There is no general agreement on the size and shape of the fibrinogen molecule. We have studied the diffusion of the fibrinogen in solution by means of dynamic light scattering, nanosecond fluorescence depolarization and analytical ultracentrifugation. The results obtained under physiological concentration, pH an ionic strength are DT = 2.0 X 10(7) cm2sec-1, DR perpendicular = 40'000 sec 1. Nanosecond fluorescence depolarization yielded DR parallel = 1.6 x 10(6) sec-1. Tentatively this value is interpreted as DR parallel, namely rotational diffusion about the major axis of the molecule. The sedimentation coefficient is 8.1 S. The hydrodynamic parameters derived from our measurements were compared with those calculated on the basis of the models proposed by Hall and Slayter, Hudry-Clergeon and Marguerie et al., Bachmann and Lederer, and Köppel. The agreement is poor even if the degree of hydration is varied within wide limits. However, satisfactory agreement can be achieved by assuming a flexible molecule of about 900 A length corresponding to two end-to-end bound trinodular structures of the Hall and Slayter type, with a nodule diameter of about 45 A. Experimental evidence indicates that the discrepancies between the different models might be due to different techniques of sample preparation leading to different conformations of the molecule.