Tenase

In coagulation, the procoagulant protein factor X can be activated into factor Xa two ways; extrinsically or intrinsically.

The activating complexes are called tenase. Tenase is a contraction of "ten" and the suffix "-ase", which means, that the complex activates its substrate (inactive factor X) by cleaving it.

Extrinsic tenase complex is made up of tissue factor, factor VII, and Ca²⁺ as an activating ion.

Intrinsic tenase complex contains the active factor IX (IXa), its cofactor factor VIII (VIIIa), the substrate (factor X), and they are activated by negatively charged surfaces (such as glass, active platelet membrane, sometimes cell membrane of monocytes). These vitamin K-dependent procoagulant factors dock to this surface through their Gla domain with Ca²⁺ bridges. This makes the activating process much faster and blocks the binding of inhibitors.