The polymerization of fibrinogen under the influence of diazomethane modification

To study the effect of the acidic amino acid residues on the physiological polymerization and clot formation of fibrinogen, the fibrinogen system was polymerized by interaction with diazomethane, a specific group reagent which modifies the carboxylic acid residues via the process of methylation. The extent of methylation of fibrinogen by diazomethane was estimated by methoxyl determination on the modified fibrinogen. Under the present experimental conditions, no significant amounts of ammonia were detected as a result of amide hydrolysis concomitant with esterification of the fibrinogen. Chemical methylation of approximately 214 residues resulted in polymerization of the fibrinogen molecule to a product which resembled the physiological clot formation. The application of paper chromatographic techniques identified the modification of other amino acid residues in addition to the methylation of the carboxylic acid groups of glutamic and aspartic acids. These results are interpreted in terms of methylation of carboxylic acid groups in fibrinogen by diazomethane providing a reduction of both negative charge and intermolecular repulsion, thereby enabling the modified fibrinogen molecules to polymerize.