The effect of gamma-carboxyglutamate residues on the enzymatic properties of the activated blood clotting factor X. I. Activity towards synthetic substrates.

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.