title: In vitro study of magnesium-calcite biomineralization in the skeletal materials of the seastar Pisaster giganteus.
abstract: The mechanisms of formation of biogenic magnesium-rich calcite remain an enigma. Here we present ultrastructural and compositional details of ossicles from the seastar Pisaster giganteus (Echinodermata, Asteroidea). Powder X-ray diffraction, infrared spectroscopy and elemental analyses confirm that the ossicles are composed of magnesium-rich calcite, whilst also containing about 0.01 % (w/w) of soluble organic matrix (SOM) as an intracrystalline component. Amino acid analysis and N-terminal sequencing revealed that this mixture of intracrystalline macromolecules consists predominantly of glycine-rich polypeptides. In vitro calcium carbonate precipitation experiments indicate that the SOM accelerates the conversion of amorphous calcium carbonate (ACC) into its final crystalline product. From this observation and from the discovery of ACC in other closely related taxa, it is suggested that substitution of magnesium into the calcite lattice through a transient precursor phase may be a universal phenomenon prevalent across the phylum echinodermata.
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Subramanyam
authors.initials: S
authors.lastname: Gayathri
authors.forename: Rajamani
authors.initials: R
authors.lastname: Lakshminarayanan
authors.forename: James C
authors.initials: JC
authors.lastname: Weaver
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Morse
authors.forename: R Manjunatha
authors.initials: RM
authors.lastname: Kini
authors.forename: Suresh
authors.initials: S
authors.lastname: Valiyaveettil
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000138:chemical synthesis*; D011232:Chemical Precipitation; D018360:Crystallography, X-Ray; D066298:In Vitro Techniques; D008274:Magnesium / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D018482:Muscle, Skeletal / Q000737:chemistry*; D013215:Starfish / Q000033:anatomy & histology / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D008903:Minerals; D002119:Calcium Carbonate; D008274:Magnesium