No strict coupling of vitamin K1 (2-methyl-3-phytyl-1,4-naphthoquinone)-dependent carboxylation and vitamin K1 epoxidation in detergent-solubilized microsomal fractions from rat liver.
NAD(P)H dehydrogenase ('DT-diaphorase', EC 1.6.99.2) and vitamin K epoxidase were removed by affinity chromatography from detergent-solubilized microsomal fractions. Thereby the microsomal fractions normally carrying out vitamin K1-dependent carboxylation of the microsomal precursor proteins of the prothrombin complex were inactivated. Purified NAD(P)H dehydrogenase added to this system restored carboxylation in the presence of vitamin K1 (2-methyl-3-phytyl-1,4-naphthoquinone) plus NADH. Vitamin K1 hydroquinone (2-methyl-3-phytyl-1,4-naphthoquinol) had no effect, in contrast with its effect in the intact system, where it can substitute for vitamin K1 plus NADH. The ability of NAD(P)H dehydrogenase to restore carboxylation in a system without vitamin K epoxidase activity shows that there is no obligatory coupling of the vitamin K1-dependent carboxylation with vitamin K1 epoxidation. These results suggest that the form of vitamin K1 that is active in the carboxylation reaction can be produced independently in two reactions: by NAD(P)H dehydrogenase in the reduction of the quinone and by vitamin K epoxidase in the epoxidation of the hydroquinone.
D000818:Animals; D002847:Chromatography, Agarose; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D008956:Models, Chemical; D011092:Polyethylene Glycols; D011498:Protein Precursors / Q000378:metabolism; D011516:Prothrombin / Q000378:metabolism; D011808:Quinone Reductases / Q000378:metabolism; D051381:Rats; D010837:Vitamin K 1 / Q000378:metabolism*
D011498:Protein Precursors; D011092:Polyethylene Glycols; D010837:Vitamin K 1; D011516:Prothrombin; D006899:Mixed Function Oxygenases; D011808:Quinone Reductases