Vitamin K Dependent Carboxylaticn Of Peptide Bound Glutamic Acid Residues

The chemical mechanism by which vitamin K promotes the posttranslational carboxylation of specific glutamic acid residues in the N-terminal region of prothrombin has not yet been elucidated. We have previously suggested that vitamin K reacts with dioxygen and carbon dioxide to form a species of active carbon. In this study we have investigated the reaction of reduced vitamin K in alcoholic solution with dioxygen in the presence and absence of carbon dioxide. We find that carbon dioxide is necessary for the rapid formation of vitamin K oxide. Vitamin K oxide was formed when either cis or trans vitamin K was used. However, trans vitamin K is specifically required in enzymatic carboxylation studies. We propose that in rat liver microsomal preparations the carboxylation of synthetic peptide substrates is coupled to the chemical epoxidation of vitamin K by the carboxylase.