title: Biochemical characterization of the serum fetuin-mineral complex.
abstract: The present study was carried out to characterize the fetuin-mineral complex (FMC), a high molecular mass complex of calcium phosphate mineral and the proteins fetuin and matrix Gla protein (MGP) that was initially discovered in serum of rats treated with etidronate and appears to play a critical role in inhibiting calcification in vivo. Fetuin purified from the FMC contains 3.3 mol of protein-bound phosphate. There is 1.3 mg of FMC/ml of serum 6 h after etidronate injection, and the FMC is 46% fetuin and 53% mineral by mass. Formation of the FMC in the first 6 h after etidronate injection does not increase serum fetuin despite the fact that 50% of serum fetuin is associated with the FMC, and clearance of the FMC in the 9-24-h interval lowers total serum fetuin by 50%. These observations suggest that the fetuin component of the FMC is derived from fetuin initially in serum and that clearance of the FMC removes the associated fetuin from circulation. One additional protein was consistently present in all preparations of the FMC, spp24 (secreted phosphoprotein 24). This 24-kDa protein is similar in domain structure to fetuin and, like fetuin and MGP, contains several residues of phosphoserine and accumulates in bone. Exogenous spp24 associated strongly with the FMC when added to serum containing it. These observations suggest that spp24 may, like fetuin and MGP, play a role in inhibiting calcification.
authors.affiliation: Division of Biology 0368, University of California-San Diego, La Jolla, CA 92093-0368, USA. pprice@ucsd.edu
authors.forename: Paul A
authors.initials: PA
authors.lastname: Price
authors.forename: Thao Minh Thi
authors.initials: TM
authors.lastname: Nguyen
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Williamson
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002130:Calcium Phosphates / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D012968:Etidronic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D010710:Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010978:Platelet Factor 4 / Q000378:metabolism; D011485:Protein Binding; D011863:Radioimmunoassay; D051381:Rats; D013696:Temperature; D013997:Time Factors; D000509:alpha-Fetoproteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D002130:Calcium Phosphates; D010710:Phosphates; D010750:Phosphoproteins; D000509:alpha-Fetoproteins; C485828:alpha-tricalcium phosphate; C091340:secreted phosphoprotein 24; C485830:tetracalcium phosphate; D010978:Platelet Factor 4; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous; D012968:Etidronic Acid; D002118:Calcium