What constitutes the prothrombinase complex?

The prothrombinase complex is crucial in the coagulation cascade, specifically in the conversion of prothrombin into thrombin. This complex is made up of several key components: Factor Xa, Factor Va, phospholipids, and calcium ions (Ca++).

Factor Xa acts as the active serine protease that, in the presence of Factor Va, catalyzes the conversion of prothrombin to thrombin. The presence of phospholipids is essential because they provide a surface for the assembly of the complex, ensuring the necessary interactions for effective catalysis. Calcium ions also play a vital role as they help to stabilize the complex and facilitate the binding of various components.

In summary, the correct answer illustrates the specific components that form the prothrombinase complex, which is essential for promoting coagulation and maintaining hemostasis. This complex is a fine example of how multiple elements work together in physiological processes.