In the liver, four of the blood clotting factors in the coagulation system (factor II, VII, IX and X) are dependent on vitamin K for their biosynthesis. The vitamin is a necessary cofactor for an enzyme complex, the vitamin K-dependent carboxylase, that converts inactive precursors of the clotting to active clotting factors. This is achieved by Gamma-carboxylation of specific glutamic acid residues in the precursor proteins. In order to function as a cofactor for the carboxylase, vitamin K must be in its reduced form, vitamin K hydroquinone. It appears that in the liver there are two independent pathways for vitamin K reduction. These are: reduction pathway I; a pathway consisting of the coumarin-sensitive enzyme vitamin K-epoxide reductase and reduction pathway II; a pathway consisting of a class of pyridine nucleotide-dependent dehydrogenases that are capable of reducing vitamin K. The pathway II enzymes are less susceptible to inhibition by coumarins and constitute an important pathway for enhanced clotting factor synthesis in cases of coumarin anticoagulant poisoning. The work that is proposed will focus on this clinically important pathway. The individual enzymes in the pathway will be purified and identified and their susceptibility to inhibition by different anticoagulant drugs studied. In addition, experiments are proposed that will measure in vitro recovery of clotting factor synthesis by high concentrations of vitamin K when pathway I is irreversibly blocked by anticoagulant drugs. The results should provide a detailed in vitro model system for the functioning of pathway II as a salvage system for clotting factor synthesis in cases of anticoagulant poisoning. The model will be tested in vivo by administering vitamin K to anticoagulated rats. A second line of work concentrates on an endogenous protein substrate for the carboxylate that follows the enzyme throughout an extensive purification procedure. Methods are proposed which will compare by peptide mapping the purified substrate protein and clotting factors II and X. It will be possible to determine if the endogenous substrate is a precursor form of factor II or X or an unrelated protein.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL032070-02
Application #
3343303
Study Section
Hematology Subcommittee 2 (HEM)
Project Start
1984-04-01
Project End
1987-03-31
Budget Start
1985-04-01
Budget End
1986-03-31
Support Year
2
Fiscal Year
1985
Total Cost
Indirect Cost
Name
Pennsylvania State University
Department
Type
Schools of Medicine
DUNS #
129348186
City
Hershey
State
PA
Country
United States
Zip Code
17033
Stanton, C; Ross, R P; Hutson, S et al. (1996) Processing and expression of rat and human clotting factor-X-encoding cDNAs. Gene 169:269-73
Stanton, C; Ross, P; Hutson, S et al. (1995) Evidence for competition between vitamin K-dependent clotting factors for intracellular processing by the vitamin K-dependent gamma-carboxylase. Thromb Res 80:63-73
Wallin, R; Stanton, C; Ross, R P (1994) Intracellular proteolytic processing of the two-chain vitamin K-dependent coagulation factor X. Thromb Res 73:395-403
Wallin, R; Stanton, C; Hutson, S M (1993) Intracellular maturation of the gamma-carboxyglutamic acid (Gla) region in prothrombin coincides with release of the propeptide. Biochem J 291 ( Pt 3):723-7
Stanton, C; Wallin, R (1992) Processing and trafficking of clotting factor X in the secretory pathway. Effects of warfarin. Biochem J 284 ( Pt 1):25-31
Loeser, R F; Wallin, R (1992) Cell adhesion to matrix Gla protein and its inhibition by an Arg-Gly-Asp-containing peptide. J Biol Chem 267:9459-62
Loeser, R; Carlson, C S; Tulli, H et al. (1992) Articular-cartilage matrix gamma-carboxyglutamic acid-containing protein. Characterization and immunolocalization. Biochem J 282 ( Pt 1):1-6
Stanton, C; Taylor, R; Wallin, R (1991) Processing of prothrombin in the secretory pathway. Biochem J 277 ( Pt 1):59-65
Loeser Jr, R F; Wallin, R (1991) Vitamin K-dependent carboxylation in articular chondrocytes. Connect Tissue Res 26:135-44
Wallin, R (1991) The effects of warfarin on HepG2 cells suggest that prothrombin and factor X interact differently with the vitamin K-dependent carboxylase in the secretory pathway. Thromb Res 62:235-40

Showing the most recent 10 out of 26 publications