Oxygen requirements for vitamin K-dependent carboxylation and epoxide formation

The requirement of vitamin K-dependent carboxylation for oxygen was determined. Carboxylation was not detected at oxygen concentrations less than 0.05 mM or in the absence of vitamin K epoxide formation. Epoxide formation was detectable at 0.05 mM and was maximal at 0.10 mM O2. Carboxylation increased with oxygen concentrations over the range of 0.10 to 0.25 mM. At oxygen concentrations at which epoxide formation was maximal, the ratio of epoxide formation to carboxylated product was approx. 3.5:1. The data are consistent with the hypothesis that an oxygenated vitamin K intermediate is required for carboxylation.