TY - JOUR
T1 - In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO 3 biomineral in crayfish gastroliths
AU - Akiva, A.
AU - Kababya, S.
AU - Balazs, Y.S.
AU - Glazer, L.
AU - Berman, A.
AU - Sagi, A.
AU - Schmidt, A.
PY - 2011/9/6
Y1 - 2011/9/6
N2 - 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.
AB - 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.
KW - Biomineralization
KW - Stabilized amorphous calcium carbonate
UR - http://www.scopus.com/inward/record.url?scp=80052558578&partnerID=8YFLogxK
U2 - 10.1073/pnas.1102608108
DO - 10.1073/pnas.1102608108
M3 - Article
C2 - 21873244
AN - SCOPUS:80052558578
SN - 0027-8424
VL - 108
SP - 14763
EP - 14768
JO - Proceedings of the National Academy of Sciences of the United States of America (PNAS)
JF - Proceedings of the National Academy of Sciences of the United States of America (PNAS)
IS - 36
ER -