The vitamin K dependent reaction.

The vitamin K's are 2-methyl-1,4-naphthoquinones. The vitamin is required for the post-translational gamma-carboxylation of glutamyl residues in precursor polypeptides. The vitamin K step in this carboxylation, however, requires not the quinone but the hydroquinone plus oxygen. Thus, the vitamin K-dependent step is a "mixed function" oxidation requiring a reducing compound plus molecular oxygen to provide a form of oxidant (e.g., a free radical, a hydroperoxide) capable of abstracting a particular, slightly labile hydrogen from a glutamyl residue, leaving this position free to accept a carbon dioxide molecule. This oxidation appears similar to that of other mixed function oxidants such as cytochrome P450 plus oxygen, ascorbic acid (with traces of ferrous iron) plus oxygen, ferrous iron plus oxygen, and a number of other systems which function in a wide variety of oxidation. Inhibition by spin-trapping agents suggests a free radical step in the vitamin K hydroquinone-dependent reaction, similar to other mixed function oxidations.