High Quality Content by WIKIPEDIA articles! Vitamin K is a group of structurally similar, fat soluble vitamins that are needed for the posttranslational modification of certain proteins required for blood coagulation and in metabolic pathways in bone and other tissue. They are 2-methyl-1,4-naphthoquinone (3-)derivatives. This group of vitamins includes two natural vitamers: vitamin K1 and vitamin K2.