Biosynthetic pathway for vitamin K-dependent production of gamma-carboxyglutamic acid

It has been hypothesized that a free cysteine residue in the carboxylase converts vitamin KH2 into a "strong base" of sufficient basicity to abstract a hydrogen from the gamma-carbon of glutamic acid (shown in red). However, the role of a free cysteine in the carboxylation reaction is uncertain. Subsequently, CO₂ is added to the gamma-carbon of glutamic acid to form gamma-carboxyglutamic acid. The activated vitamin K species collapses into vitamin K epoxide and is recycled back to vitamin KH2, following the action of two vitamin K reductases, one of which is inhibited by warfarin.