Physiological Functions And Pharmacologicalactions

Phylloquinone and menaquinones are virtually devoid of pharmacodynamic activity. However, in subjects deficient in vitamin K, the vitamin performs its normal physiological function: to promote the biosynthesis of the g-carboxy-glutamate (Gla) forms of factors II (prothrombin), VII, IX, and X, anticoagulant proteins C and S, protein Z (a cofactor to the inhibitor of Xa), the bone Gla protein osteocalcin, matrix Gla protein, and growth arrest-specific protein 6 (Gas6). Figure 54-6 summarizes the coupling of the vitamin K cycle with glutamate carboxylation. Vitamin K, as KH2, the reduced hydroquinone, is an essential cofactor for g-glutamyl carboxylase. Using KH2, O2, CO2, and the glutamate-containing substrate, the enzyme forms a g-carboxy-glutamatyl protein (Gla protein) and concomitantly, the 2,3-epoxide of vitamin K. A coumarin-sensitive 2,3-epoxide reductase regenerates KH2. The g-glutamyl carboxylase and epoxide reductase are integral membrane proteins of the endoplasmic reticulum and function as a multicomponent complex. Two natural mutations in g-glutamyl carboxylase lead to bleeding disorders. With respect to proteins affecting blood coagulation, these reactions occur in the liver, but g-carboxylation of Glu also occurs in lung, bone, and other cell types.

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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