Prepared from Bovine Factor IX by activation with Bovine Factor Xla, this Bovine Factor Xla is removed after activation. Complete activation is observed by SDS-PAGE. The Factor Xla activates FIX in a two-step reaction. In the first step, an internal Arg-Ala bond is cleaved, and in the second step, an Arg-Val bond is cleaved. The second cleavage leads to the liberation of an activation peptide from the NH2-terminal portion of the heavy chain to produce factor IXaβ.