In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO 3 biomineral in crayfish gastroliths

A. Akiva, S. Kababya, Y.S. Balazs, L. Glazer, A. Berman, A. Sagi, A. Schmidt

Research output: Contribution to journalArticleAcademicpeer-review

55 Citations (Scopus)

Abstract

Bioavailable calcium is maintained by some crustaceans, in particular freshwater crayfish, by stabilizing amorphous calcium carbonate (ACC) within reservoir organs-gastroliths, readily providing the Ca 2+ needed to build a new exoskeleton. Despite the key scientific and biomedical importance of the in situ molecular- level picture of biogenic ACC and its stabilization in a bioavailable form, its description has eluded efforts to date. Herein, using multinuclear NMR, we accomplish in situ molecular-level characterization of ACC within intact gastroliths of the crayfish Cherax quadricarinatus. In addition to the known CaCO 3, chitin scaffold and inorganic phosphate (Pi), we identify within the gastrolith two primary metabolites, citrate and phosphoenolpyruvate (PEP) and quantify their abundance by applying solution NMR techniques to the gastrolith "soluble matrix." The long-standing question on the physico-chemical state of ACC stabilizing, P-bearing moieties within the gastrolith is answered directly by the application of solid state rotational-echo double-resonance (REDOR) and transferred- echo double-resonance (TEDOR) NMR to the intact gastroliths: Pi and PEP are found molecularly dispersed throughout the ACC as a solid solution. Citrate carboxylates are found 2+. The high abundance and extensive interactions of these molecules with the ACC matrix identify them as the central constituents stabilizing the bioavailable form of calcium. This study further emphasizes that it is imperative to characterize the intact biogenic CaCO 3. Solid state NMR spectroscopy is shown to be a robust and accessible means of determining composition, internal structure, and molecular functionality in situ.

Original languageEnglish
Pages (from-to)14763-14768
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America (PNAS)
Volume108
Issue number36
DOIs
Publication statusPublished - 6 Sep 2011
Externally publishedYes

Keywords

  • Biomineralization
  • Stabilized amorphous calcium carbonate

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