Involved in vitamin K metabolism. Can reduce inactive vitamin K 2,3-epoxide to active vitamin K, and may contribute to vitamin K- mediated protection against oxidative stress. Plays a role in vitamin K-dependent gamma-carboxylation of Glu residues in target proteins. {ECO:0000269|PubMed:21367861, ECO:0000269|PubMed:23928358, ECO:0000269|PubMed:24532791}. This is the function of VKORC1L1 (vitamin K epoxide reductase complex subunit 1L1, ENSG00000196715).