The effect of γ-carboxyglutamate residues on the enzymatic properties of the activated blood clotting factor X

Abstract

The esterolytic and amidolytic properties of activated blood coagulation factor X (factor Xa) and the analogous decarboxy species were compared in order to find out if the gamma-carboxyglutamic acid residues influence the function of the active centre. It was found that the two proteins (1) showed similar kinetic parameters when titrated with p-nitrophenyl-p'-guanidinobenzoate hydrochloride (2) had a similar Km and kcat for various synthetic chromogenic tri- and tetrapeptides and (3) were inhibited in the same way by benzamidine. Further it was observed that (4) Ca2+ inactivates factor Xa, but has no influence on the amidase activity of decarbyxyfactor Xa (5) factor V prevents Ca2+-induced inactivation of factor Xa but does not influence the amidase activity of both factor Xa and decarboxyfactor Xa. We conclude that the interaction of the gamma-carboxyglutamic acid residues with Ca2+ in factor X has no measurable influence on the properties of the active site per se.

Factor X Fusion Proteins: Improved Production and Use in the Release in Vitro of Biologically Active Hirudin from an Inactive α-Factor–Hirudin Fusion Protein

“…Although the posttranslational ␥-carboxylation of glutamate residues is essential for the procoagulant activity of FX (18), neither the Gla domain nor the E1 domain is required for the proteolytic activity of FXa (19). In addition to the Gla domain playing a role in intracellular trafficking (2), incomplete ␥-carboxylation can lead to intracellular degradation of Gla-containing proteins (20,21).…”