<prompt> Conversion of Prothrombin to thrombin requiresCaVa, CaV, X, CaX, V, XII, Ca  <response>: In the presence of tissue phospholipids PL and calcium ions, activated Factor X Xa combines with Factor Va to form prothrombin activator which initiates the conversion of prothrombin to thrombin.Factor V, X, and XII are activated and involved in other steps of intrinsic pathway.Ref: Ganong;s review of medical physiology, 23rd edition, page: 533 