Vitamin K is required for: March 2005

Ans. C: Carboxylation The function of vitamin K in the cell is to conve glutamate in proteins to gamma-carboxyglutamate (gla). Within the cell, vitamin K undergoes electron reduction to a reduced form of vitamin K (called vitamin K hydroquinone) by the enzyme vitamin K epoxide reductase (or VKOR). Another enzyme then oxidizes vitamin K hydroquinone to allow carboxylation of Glutamate to gamma carboxyglutamate; this enzyme is called the gamma-glutamyl carboxylase or the vitamin K-dependent carboxylase. The carboxylation reaction will only proceed if the carboxylase enzyme is able to oxidize vitamin K hydroquinone to vitamin K epoxide at the same time; the carboxylation and epoxidation reactions are said to be coupled reactions.