Some aspects of the polymerization of fibrinogen

The polymerization of activated fibrinogen takes place in two stages. First, the monomer units form intermediate polymers with twice the original cross‐section area and about eight times the original length. The polymers have been detected under a variety of conditions between p H 6.1 and 10. The polymerization geometry is believed to be lateral dimerization with a staggered configuration, determined by a pattern of electrical charges. The negatively charged groups, though unidentified, appear to be near histidine residues, as deduced from the dependence of polymerization on p H. The positively charged groups, from this and other evidence, appear to be α‐amino groups. Second, the intermediate polymers unite to form the strands of the fibrin network. This association appears to involve nonpolar groups, and the width of the final strands, unlike that of the intermediate polymer, depends markedly on the net charge as determined by the p H.