Vitamin K-dependent carboxylation. Evidence that at least two microsomal dehydrogenases reduce vitamin K1 to support carboxylation.

It has been shown that NAD(P)H dehydrogenase (EC 1.6.99.2) reduces vitamin K1 and can support the [vitamin K1 + NADH]-dependent carboxylation reaction in rat liver microsomes (Wallin, R., Gebhardt, O., and Prydz, H. (1978) Biochem. J. 169, 95-101). Antibodies were raised in rabbits against the purified enzyme from liver cytosol and used to study the importance of NAD(P)H dehydrogenase in the vitamin K-dependent carboxylation reaction. The antibodies neutralized the warfarin-sensitive NAD(P)H dehydrogenase activity in Triton X-100-solubilized microsomes; however, they neutralized only 45% of the total [vitamin K1 + NADH]-dependent carboxylation activity. Chromatography on protein A-sepharose showed that the remaining carboxylase activity was not the result of soluble antigen-antibody complexes. The data presented support the conclusion that the microsomal preparation also contains a non-warfarin-sensitive dehydrogenase(s) that, in addition to NAD(P)H dehydrogenase, can reduce vitamin K1 to support the carboxylation reaction.