Dioxygen and the vitamin K-dependent synthesis of prothrombin

It has been shown that bovine erythrocyte superoxide dismutase inhibits the gamma-carboxylation of glutamyl residues in the precursor of prothrombin and in a related synthetic peptide by a vitamin K-dependent rat liver microsomal carboxylase. In the same conditions a simple copper(II) tyrosinyl complex also inhibits the carobxylation. The formation of the vitamin K epoxide by the same systems is inhibited by both superoxide dismutase and catalase. It is suggested that the formation of the epoxide is a process distinct from carboxylation, representing perhaps a protective mechanism against the superoxide ion, or species derived therefrom, generated by the reaction of reduced vitamin K with dioxygen. Furthermore, the possibility that the carboxylating species is formed by the reaction of the superoxide ion, or species derived therefrom, with carbon dioxide, is proposed.