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Osteonectin
ELISA
 Osteonectin
(SPARC, BM-40) is a 32,700 molecular weight, Ca2+ion-binding glyco-protein which is a synthetic product of osteoblasts (1-3), endothelial cells (4-5), and megakaryocytes (6). Although the exact biological function of osteonectin is not known, several lines of evidence suggest that osteonectin is intimately involved in tissue remodeling both from the perspective of bone metabolism and endothelial cell proliferation and repair (7). Therefore, the quantitative analysis of this protein could serve as a useful marker for the researcher studying the biochemical processes governing vascular wound repair, platelet activation, and skeletal metabolism. The osteonectin (SPARC) immunoassay is a competitive-type enzyme-linked immunosorbant assay (ELISA). The assay utilizes a purified osteonectin standard derived from human platelets (8,9). A standard curve is generated based upon the competition between fluid-phase osteonectin and an osteonectin-biotin conjugate for an immobilized monoclonal antibody. Solid-phase antibody/biotinyl-osteonectin complexes are detected using avidin-peroxidase. A colorimetric signal, which is inversely proportional to the amount of osteonectin in the fluid-phase, is obtained following the addition of chromogenic substrate. The HTI osteonectin immunoassay utilizes a monoclonal antibody which cross-reacts with osteonectin derived from several different sources (8-10). The epitope of the antibody is directed to a central region of human osteonectin (11) where the amino acid sequence as deduced from the corresponding cDNA of several different species and tissue sources is highly conserved (12-16).
Based upon the relative concentrations of osteonectin among the tissues, the vast majority of circulating osteonectin likely originates from bone and platelets (8,17-19). Bone and platelet-derived osteonectin are identical in terms of amino acid sequence but differ with respect to N-linked glycosylation (20,21). Immunological recognition within this assay does not depend on the extent of N-linked glycosylation. The use of a citrate or heparin-based anticoagulant containing platelet inhibitors is required to minimize the contribution of osteonectin in plasma due to platelet activation during phlebotomy.
RELATED
PRODUCTS: Human
Osteonectin; Bovine
Osteonectin, Anti-Osteonectin antibody
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References
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