VKOR and GGCX activity for the various cell lines. (A) Vitamin K reduced from vitamin K epoxide by the VKOR was measured as previously described (n = 3).⁶  HEK293-FX (A6): HEK293 cells over-expressing factor X. HEK293-FX (A6)–VKOR: HEK293 cells overexpressing both factor X and the VKOR. HEK293-FX (A6)–GGCX: HEK293 cells overexpressing both factor X and GGCX. HEK293-FX (A6)–VKOR-GGCX: HEK293 cells overexpressing factor X, VKOR, and GGCX. (B) GGCX activity for the following cell lines as defined in panel A: HEK293-FX (A6), HEK293-FX (A6)–VKOR, HEK293-FX (A6)–GGCX, HEK293-FX (A6)–VKOR-GGCX. GGCX activity toward the pentapeptide substrate FLEEL was measured as described (n = 3). Data are presented as mean ± SD.¹