Evidence for vitamin K semiquinone as the functional form of vitamin K in the liver vitamin K-dependent protein carboxylation reaction

Abstract

The protein carboxylating system derived from vitamin K-deficient rat liver microsomes functions in detergent solution if vitamin K 1, NADH, dithiothreitol, CO 2 and O 2 are added. The requirements for added NADH, dithiothreitol and O 2 are all eliminated by the use of vitamin K 1 hydroquinone in place of quinone. The use of the hydroquinone gives a more rapid reaction and a higher yield than does the quinone plus reducing system. The reaction proceeding from either the vitamin K 1 quinone or hydroquinone is blocked by the spin-trapping agent, 5,5-dimethyl-l-pyrroline-N-oxide, suggesting that the active form of vitamin K is the semiquinone.