THE ULTRASTRUCTURE OF FIBRINOGEN CARACAS-II MOLECULES, FIBERS, AND CLOTS

Fibrinogen Caracas II is an abnormal fibrinogen involving the mutation of A alpha serine 434 to N-glycosylated asparagine. Some effects of t his mutation on the ultrastructure of fibrinogen Caracas II molecules, fibers, and clots were investigated by electron microscopy. Electron microscopy of rotary shadowed individual molecules indicated that most of the alpha C domains of fibrinogen Caracas II do not interact with each other or with the central domain, in contrast to control fibrinog en, Negatively contrasted Caracas II fibers were thinner and less orde red than control fibers, and many free fiber ends were observed, Scann ing electron microscopy of whole clots revealed the presence of large pores bounded by local fiber networks made up of thin fibers. Permeati on experiments also indicated that the average pore diameter was large r than that of control clots. The viscoelastic properties of the Carac as II clot, as measured by a torsion pendulum, were similar to those o f control clots. Both the normal stiffness and increased permeability of the Caracas II clots are consistent with the observation that subje cts with this dysfibrinogenemia are asymptomatic.