The formation of beta fibrin requires a functional a site.

We used recombinant fibrinogens in which the a site is disrupted to examine beta-fibrin formation in the absence of a functional a site. Our variants have only b sites available, and they showed no evidence of fibrin polymer formation after cleavage of FpB with venzyme. We conclude that B-b interactions are not strong enough to induce clot formation. Our studies do not rule out the involvement of b in the formation of beta-fibrin, yet they do provide evidence that a is likely to be essential in the formation of beta-fibrin.