Oriented fibrin gels formed by polymerization in strong magnetic fields

Abstract

Fibrinogen is a soluble plasma protein which, after cleavage by the specific proteolytic enzyme thrombin, polymerizes to form the filamentous fibrin network during blood clotting (see refs 1 and 2 for reviews). Fibrinogen has a molecular weight of 340,000 and is composed of two identical halves, each containing three peptide chains designated A alpha, B beta and gamma. Fibrin monomers are produced by thrombin which releases the small negatively charged fibrinopeptides A and B. The overall shape of the fibrinogen molecule has not been unequivocally established. The trinodular, elongated (approximately 450 A long) structure proposed by Hall and Slayter is the most widely accepted model and it has obtained additional support from recent work. Fibrin monomers are also about 450 A long and in fibres they probably have a half-staggered arrangement along the axis. The fibres are an assembly of protofibrils whose structure and packing are not reliably known. We report here that highly oriented fibrin gels are formed when polymerization takes place slowly in a strong magnetic field. It is shown that the protofibrils pack into a three-dimensional crystalline lattice. We introduce magnetically induced birefringence as a potential tool for studying polymerization and briefly speculate on the applications of strong magnetic fields.

Sensitivity of MRI resonance frequency to the orientation of brain tissue microstructure

“…Anisotropic magnetic susceptibility is a phenomenon commonly seen in crystals of highly anisotropic atomic structure. It also has been noted in constituents of biological tissues, including muscle fibers (17), retinal rods (18), nucleic acids (19), proteins (20)(21)(22)(23), and lipid bilayers (24)(25)(26)(27). Because the proteins and lipid bilayers associated with white matter fibers are highly ordered, anisotropic susceptibility may have contributed to our present findings.…”

Protein crystals orientation in a magnetic field

“…This explains why proteins and synthetic polypeptides exhibit magnetic orientation with the -helices parallel to the magnetic ®eld. In the literature, most of the studies focus on the magnetic birefringence (Cotton±Mouton effect) of aromatic or aliphatic compounds (Lonsdale, 1939) or biological systems (Neugebauer et al, 1977;Torbet et al, 1981;Yamagishi, 1990). The diamagnetic anisotropy is characterized by observation of the formation of oriented ®brin, of small crystals or by the anisotropy of a scattering pattern.…”

Evidence of the hexagonal columnar liquid-crystal phase of hard colloidal platelets by high-resolution SAXS

“…Usually, oriented samples are prepared by applying an external field, e.g. magnetic fields [47][48][49][50][51] and shear flow [52][53][54]. Here, we use sterically stabilised colloidal gibbsite platelets with non-adsorbing polymer as a depleting agent.…”