Summary
The trimethyl oxonium ion specifically modified the free carboxyl groups of fibrinogen.
This esterification process resulted in the polymerization of the modified fibrinogen
molecule with the production of a polymeric material that resembled the physiologically
formed fibrin clot. The extent of methylation of fibrinogen was evaluated by methoxyl
determination at each step of the polymerization process. The modified fibrinogen
polymerized in approximately ten min with a minimum number of methyl groups being
incorporated into the fibrinogen molecule. In this manner, it was shown that modification
of carboxyl groups in the fibrinogen by a group-specific methylating agent results
in polymerization of the fibrinogen.
The sites of methylation were ascertained by chromatographic analysis which resulted
in the identification of β-methyl aspartic acid and γ-methyl glutamic acid derivatives
of the fibrinogen. The analytical methods applied were not able to detect the methylation
of any additional amino acid residues in the polymerized-methylated fibrinogen. Based
on this experimental data, it was formulated that the methylation of fibrinogen involved
the esterification of the carboxyl groups of aspartic and glutamic acid with the resultant
reduction of negative repulsion between the fibrinogen molecules and thereby culminated
in the polymerization of the modified fibrinogen.
Keywords Fibrinogen - Trimethyl oxonium ion - Carboxyl groups - Polymerization - Methylation
