Using reduced vitamin K, oxygen, and carbon dioxide, gamma-glutamyl carboxylase post-translationally modifies certain glutamates by adding carbon dioxide to the gamma position of those amino acids. In vertebrates, the modification of glutamate residues of target proteins is facilitated by an interaction between a propeptide present on target proteins and the gamma-glutamyl carboxylase [1].

1: Identification of a Drosophila vitamin K-dependent gamma-glutamyl carboxylase. Li T, Yang CT, Jin D, Stafford DW; J Biol Chem 2000;275:18291-18296. PMID:10748045