Calcified Tissue International

, Volume 72, Issue 5, pp 610–626

Phosphate Ions in Bone: Identification of a Calcium–Organic Phosphate Complex by 31P Solid-State NMR Spectroscopy at Early Stages of Mineralization

  • Y. Wu
  • J. L. Ackerman
  • E. S. Strawich
  • C. Rey
  • H. -M. Kim
  • M. J. Glimcher


Previous 31P cross-polarization and differential cross-polarization magic angle spinning (CP/MAS and DCP/MAS) solid-state NMR spectroscopy studies of native bone and of the isolated crystals of the calcified matrix synthesized by osteoblasts in cell culture identified and characterized the major PO4−3 phosphate components of the mineral phase. The isotropic and anisotropic chemical shift parameters of the minor HPO4−2 component in bone mineral and in mineral deposited in osteoblast cell cultures were found to differ significantly from those of brushite, octacalcium phosphate, and other synthetic calcium phosphates. However, because of in vivo and in vitro evidence that phosphoproteins may play a significant role in the nucleation of the solid mineral phase of calcium phosphate in bone and other vertebrate calcified tissues, the focus of the current solid-state 31P NMR experiments was to detect the possible presence of and characterize the phosphoryl groups of phosphoproteins in bone at the very earliest stages of bone mineralization, as well as the possible presence of calcium-phosphoprotein complexes. The present study demonstrates that by far the major phosphate components identified by solid-state 31P NMR in the very earliest stages of mineralization are protein phosphoryl groups which are not complexed with calcium. However, very small amounts of calcium-complexed protein phosphoryl groups as well as even smaller, trace amounts of apatite crystals were also present at the earliest phases of mineralization. These data support the hypothesis that phosphoproteins complexed with calcium play a significant role in the initiation of bone calcification.


Phosphoproteins Bone 31P NMR Calcification Apatite 


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • Y. Wu
    • 1
    • 2
  • J. L. Ackerman
    • 1
    • 2
  • E. S. Strawich
    • 1
  • C. Rey
    • 3
  • H. -M. Kim
    • 4
  • M. J. Glimcher
    • 1
  1. 1.Laboratory for the Study of Skeletal Disorders and Rehabilitation, Department of Orthopaedic SurgeryChildren’s Hospital, Harvard Medical School, Boston, MA 02115USA
  2. 2.Biomaterials Laboratory, NMR Center, Department of RadiologyMassachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129USA
  3. 3.Centre Interuniversitaire de Recherche et d’Ingénierie des Matériaux, INPT, ENSCT, UMR CNRS 5085, 31400 ToulouseFrance
  4. 4.Laboratory of Hard Tissue EngineeringDepartment of Oral Anatomy, College of Dentistry, Seoul National University, SeoulSouth Korea 110-749

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