Inhibition of the fibrinogen-plasmin reaction by ω-aminocarboxylic acids and alkylamines

We measured (with the pH stat) the rat of hydrolysis of fibrinogen and lysine methyl ester by plasmin (EC 3.4.4.1.4) and calculated the maximal velocity (v_max) for both reactions. The v_max for the lysine methyl ester-plasmin reaction is 1.5 times greater than the v_max for the fibrinogen-plasmin reaction at pH 7.0, and at 23°. The same enzyme preparation and solvent ionic strength were used in both reactions.

A new method for measuring proteolysis of fibrinogen by plasmin is reported. This method is based on the precipitation of non-hydrolyzed fibrinogen by 9% ethanol. With this method we investigated inhibition of the fibrinogen-plasmin reaction by ω-aminocarboxylic acids and analogues of some of the 3,4,5 and 6-carbon members. Glycine, β-alanine, γ-aminobutyric acid, glutaric acid, valeric acid, cadaverine and lysine did not inhibit with concentrations less than 10 mM (K_i>10 mM). Competitive inhibition was found with δ-aminovaleric acid (K_i = 4.7 mM), ϵ-aminocaproic acid (K_i = 2.8 mM), ω-aminocaprylic acid (K_i = 1.0 mM), propylamine (K_i = 3.3 mM) < butylamine (K_i = 3.0 mM) and amylamine (K_i = 1.0 mM). Inhibition probably occurs at the active center and is probably due to both electrostatic and hydrophobic bonding of the inhibitor to the enzyme because inhibition is competitive and because inhibition is dependent on the positive charge and increases with increasing chain length of either the ω-aminocarboxylic acid or the alkylamine.