GO:0047057:   vitamin-K-epoxide reductase (warfarin-sensitive) activity
Catalysis of the reaction: 2-methyl-3-phytyl-1,4-naphthoquinone + oxidized dithiothreitol + H2O = 2,3-epoxy-2,3-dihydro-2-methyl-3-phytyl-1,4-naphthoquinone + 1,4-dithiothreitol.