Osteocalcin

In bone, three proteins have been described which are vitamin K-dependent, osteocalcin (bone Gla protein), matrix Gla protein (MGP), and protein S. Osteocalcin is synthetized by osteoclasts, regulated by the active form of vitamin D, calcitriol. Its capacity to bind calcium needs a vitamin K-dependent y-carboxylation of three glutamic acid residues. The calcium binding capacity of osteocalcin indicates a possible role in bone mineralization, but its exact function is still unclear. However, it is widely used as a serum marker for bone mineralization. Protein S, mainly a coagulant, is also vitamin-K dependent and synthesized in the liver. Children with... 

This illness is mainly characterized by an age-related bone loss. The detection of osteocalcin in bone was the starting point for a series of studies on the role of vitamin K-dependent proteins in bone development and maintenance and on possible supplemantation therapies. Epidemiologic studies found differences in the risk of hip fractures depending on the dietary vitamin K... 

Supplementation with high doses of vitamin K1 (1 mg/day for 14 days) or MK-4 (45 mg/day) resulted in decreased levels of undercarboxylated osteocalcin and increase of bone formation markers and in a significant reduction in bone loss, respectively. Using such high doses, any kind of effects besides vitamin K can not yet be ruled out and have to be further elucidated by long term studies. An overview can be found in a review by Palacios [4]. 

In contrast to the formation and calcification of bones, vitamin K seems to lower the risk of aortic calcification. The mechanisms for these antagonistic effects is not known but a participation of osteocalcin (expressed in artherosclerotic plaques) as well as of matrix Gla protein (MGP) are discussed. In addition, the vitamin K epoxide reductase complex seems to be involved [5]. 

The cell growth was much faster on the chitosan-hydroxyapatite scaffolds with the glass than on the chitosan-hydroxyapatite scaffold without the glass. The total protein content of cells increased over time on both composites. The cells on the chitosan-hydroxyapatite-glass also expressed significantly higher amount of alkaline phosphatase at days 7 and 11 and osteocalcin at day 7 than those on chitosan-hydroxyapatite [165]. 

There are approximately 200 other proteins present in bone, though most of them are present only in trace amounts (Delmas et al., 1984 Linde et al., 1980, as cited in van Klinken, 1991). The second most common bone protein, osteocalcin, comprises 1-2 weight % of total fresh bone. Osteocalcin bonds with both the bone mineral fraction and bone collagen, but it seems to be unstable in solutions. Due to its small molecular size and strong mineral stabilization, osteocalcin can survive up to 50.000 years (C.l. Smith et al., 2005), and it may offer an alternative to the use of collagen in paleoenvironmental stable isotope research. However, osteocalcin s role and importance in this field of study has yet to be defined (Collins et al., 2002). 

Treatment of pregnant women with warfarin can lead to fetal bone abnormalities (fetal warfarin syndrome). Two proteins are present in bone that contain y-carboxygluta-mate, osteocalcin and bone matrix Gla protein. Osteocalcin also contains hydroxyproHne, so its synthesis is dependent on both vitamins K and C in addition, its synthesis is induced by vitamin D. The release into the circulation of osteocalcin provides an index of vitamin D stams. 

A number of iron-containing, ascorbate-requiring hydroxylases share a common reaction mechanism in which hydroxylation of the substrate is linked to decarboxylation of a-ketoglutarate (Figure 28-11). Many of these enzymes are involved in the modification of precursor proteins. Proline and lysine hydroxylases are required for the postsynthetic modification of procollagen to collagen, and prohne hydroxylase is also required in formation of osteocalcin and the Clq component of complement. Aspartate P-hydroxylase is required for the postsynthetic modification of the precursor of protein C, the vitamin K-dependent protease which hydrolyzes activated factor V in the blood clotting cascade. TrimethyUysine and y-butyrobetaine hydroxylases are required for the synthesis of carnitine. 

Osteocalcin (bone Gla protein) Contains y-carboxyglutamate residues that bind to hydroxyapatite. Bone-specific. 

Understand the mechanism of Pb2+ National Institute of toxicity at the molecular level, in bone, Environmental Health by comparing precise structural and Sciences functional data of ca2+ - and Pb2+ -osteocalcin... 

Bronckers, A.J.J., Gay, S., Finkelman, R.D., and Butler, W.T. (1987) Immunolocalization of Gla proteins (osteocalcin) in rat tooth germs Comparison between indirect immunofluorescence, peroxidase-antiperoxidase, avidin-biotin-peroxidase complex, and avidin-biotin-gold complex with silver enhancement./. Histochem. Cytochem. 35, 825-830. 

Oncomodulin Osteocalcin regulator (374) P-Parvalbumin (375) Extracellular protein abundant in bone and in dentin (376,377)... 

A complete physical examination and laboratory analysis are needed to rule out secondary causes and to assess kyphosis and back pain. Laboratory testing may include complete blood count, liver function tests, creatinine, urea nitrogen, calcium, phosphorus, alkaline phosphatase, albumin, thyroid-stimulating hormone, free testosterone, 25-hydroxyvitamin D, and 24-hour urine concentrations of calcium and phosphorus. Urine or serum biomarkers (e.g., cross-linked N-telopeptides of type 1 collagen, osteocalcin) are sometimes used. 

Levormeloxifene induces an increase in lumbar and tibial bone mass in a rat model and is associated with a decrease in osteocalcin and cholesterol levels, while it has a neutral effect on the uterus (Bain et al. 1997 Nowak et al. 1998). In monkeys, a decrease in bone remodeling with prevention of bone loss has... 

Nowak J, Hornby SB, Andersen A, Siogren T, Feslersen U, Christiensen ND (1998) Effect of 12 month treatment with levormeloxifene on bone, serum cholesterol, osteocalcin and uterus in ovariectomized rat. In AS-BMR IBMS joint meeting, San Francisco, December 1998. Bone 23(Suppl) S610... 

Williams DC, Paul DC, Black LJ (1991) Effects of estrogen and tamoxifen on serum osteocalcin levels in ovariectomized rats. Bone Miner 14 205-220... 

P. V. Hauschka and S. A. Carr, Calcium-dependent alpha-helical structure in osteocalcin, Biochemistry 21, 2538-2547 (1982). 

As markers of osteogenie differentiation, high activity of alkaline phosphatase, production of collagen 1 and non-collagenous calcium-binding ECM glycoproteins osteocalcin and osteopontin are currently evaluated [14-17,24-27,37,47],... 

Vitamin K promotes the hepatic y-car-boxylation of glutamate residues on the precursors of factors II, VII, IX, and X, as well as that of other proteins, e.g., protein C, protein S, or osteocalcin. Carboxyl groups are required for Ca +-mediat-ed binding to phospholipid surfaces (p, 142). There are several vitamin K derivatives of different origins Ichlorophyllous plants I<2 from gut bacteria and I<3 (menadione) synthesized chemically. All are hydrophobic and require bile acids for absorption. 

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