In vitro prothrombin synthesis from a purified precursor protein. I. Development of a bovine liver cell-free system.

In the absence of vitamin K many mammals generate proteins (PIVKAs) which axe immunologically identical to the vitamin K-dependent clotting factors but which lack thet functional activity [1]. At the moment of their discovery in 1963 121 It was already supposed that PIVKAs were precursors of the vitamin K-dependent coagulation factors. After the discovery by Stenflo and coworkers [3] that the 7-calboxyl gloups present in 10 glutamic acid residues of prothrombin account for the difference between PMA-II and prothrombin, it was to be expected that the vitamin K-dependent system brought ahout the carboxylation of PIVKA. Suttie and coworkers [4,5] showed that liver microsomes from vitamin K-deficient rats mediate in the incorporation of l4C-Iabeled COz and generate factor II activity, supposedly from an endogenous plecursor. In the present paper we describe the conversion of purified PIVKA-II into prothrombin by a cell-free system derived from normal bovine liver.