An Antimetabolic Action of Vitamin K

Abstract

IN recent studies in vivo and in vitro, we have shown that the K vitamins (K₁, K₂, phthiocol, menadione and ‘Synkavit’) inhibit the synthesis of nicotinic acid at the stage 3-hydroxyanthranilic acid→quinolinic acid. We suggested that the mechanism of inhibition is competition between vitamin K and 3-hydroxyanthranilic acid, that is, the K vitamins exert antimetabolitic action on the substrate of the reaction catalysed by 3-hydroxyanthranilic acid oxidase. On the basis of this hypothesis, investigations were undertaken to determine if the inhibition of 3-hydroxyanthranilic acid oxidase produced in vivo by administration of menadione or ‘Synkavit’ could be reversed by subsequent administration of 3-hydroxyanthranilic acid. The results of these experiments demonstrated the capacity of 3-hydroxyanthranilic acid to overcome the inhibitory effect of vitamin K.