Human Coagulation Factor IX (Factor 9) is a vitamin K-dependent coagulation factor that circulates in the blood as an inactive zymogen. This factor is converted to an active form by factor XIa, which excises the activation peptide and thus generates a heavy chain and a light chain held together by one or more disulfide bonds. The role of this activated factor IX in the blood coagulation cascade is to activate factor X to its active form through interactions with Ca+2 ions, membrane phospholipids, and factor VIII.

Native Human Factor IXa is prepared from Human Factor IX by activation with Bovine Factor XIa (which is removed after activation). Factor XIa activates Factor IX in a twostep reaction. In the first step, an internal Arg-Ala bond is cleaved, and in the second step, an Arg-Val bond is cleaved, resulting in Factor IXa-alpha. The second cleavage leads to the liberation of an activation peptide from the NH2-terminal portion of the heavy chain to produce Factor IXa-beta. Factor IXa-alpha has about half the coagulant activity of Human Factor IXa-beta.