Proteolysis of blood coagulation factor X by activated factor X: Difference between the bovine and human proteins

Abstract

Factor X is a plasma glycoprotein that is involved in both the intrinsic and extrinsic pathway of blood coagulation. During the coagulation process, factor X is converted to factor Xa (EC 3.4.21.6), a serine protease catalysing the activation of prothrombin and the enzymatic conversion of several other coagulation factors [ 1,2]. One of the substrates of factor Xa is its zymogen, factor X. In the bovine system, the cleavage of factor X by factor Xa can result in the activation of factor X [3-51. In the human system however, factor Xa cleaves a peptide from factor X that contains the active-site serine residue [6]. Thus, the bovine and human system differ with respect to the effect of factor Xa on factor X (activation vs inactivation). Here, the proteolysis of factor X by factor Xa in various combinations of human and bovine proteins is described. We conclude that the enzymes of both species have similar substrate specificities and that structural differences between the human and bovine zymogen account for the different autocatalytic pathways.