Mediates the vitamin K-dependent carboxylation of glutamate residues to calcium-binding gamma-carboxyglutamate (Gla) residues with the concomitant epoxidation of vitamin K hydroquinone to vitamin K epoxide (PubMed:17073445, PubMed:39880952, PubMed:39880037). Couples epoxidation and carboxylation in the same active site (PubMed:39880952, PubMed:39880037). Catalyzes gamma-carboxylation of blood coagulation factors (F2, F7, F9 and F10) and anticoagulants such as PROC, which are essential for thrombosis(PubMed:17073445, PubMed:39880037). Catalyzes gamma-carboxylation of osteocalcin/BGLAP, which is essential for bone metabolism (PubMed:17073445, PubMed:39880952). Catalyzes gamma- carboxylation of matrix Gla protein (MGP) and other transmembrane gamma-Gla proteins such as PRRG2, which are essential for calcium homeostasis and haemostasis (PubMed:17073445, PubMed:39880037). {ECO:0000269|PubMed:17073445, ECO:0000269|PubMed:39880037, ECO:0000269|PubMed:39880952}. This is the function of GGCX (gamma-glutamyl carboxylase, ENSG00000115486).