Post-translational carboxylation of preprothrombin

The determination of the sites of possible regulation in the formation of an active enzyme protein was only possible after the overall pathway of active enzyme synthesis had been established. Regulation may be via the triplet code at the genetic transcription level, or at the translation level from messenger RNA to protein or at a post-translational level via chemical modification and/or polypeptide aggregation. The fact that the role of vitamin K in the formation of the normally pro-active forms of the coagulation proteins (II, VII, IX, and X) was post- translational was shown by Goswami and Munro (1) in 1962, and further confirmed by Hill, et al. (2), Babior (3), Lowenthal and Simmons (4), Ranhotra, et al. (5), and Shah and Suttie (6). In these studies total enzyme activity (prothrombin) recovery in vivo was obtained following administration of vitamin K to vitamin K deficient (7,8) rats which had received protein synthesis blocking agents. R. E. Olson, et al. (9–12) stated that vitamin K functioned in prothrombin synthesis at a genetic or translation level on the basis of no response to the vitamin after synthesis of protein was inhibited. This, however, became untenable with the finding of carboxylation as the vitamin K dependent step (13–16) in prothrombin ‘completion’.