title: Phase transitions in biogenic amorphous calcium carbonate.
abstract: Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro.
authors.affiliation: Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, WI 53706, USA.
authors.forename: Yutao U T
authors.initials: YU
authors.lastname: Gong
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Killian
authors.forename: Ian C
authors.initials: IC
authors.lastname: Olson
authors.forename: Narayana P
authors.initials: NP
authors.lastname: Appathurai
authors.forename: Audra L
authors.initials: AL
authors.lastname: Amasino
authors.forename: Michael C
authors.initials: MC
authors.lastname: Martin
authors.forename: Liam J
authors.initials: LJ
authors.lastname: Holt
authors.forename: Fred H
authors.initials: FH
authors.lastname: Wilt
authors.forename: P U P A
authors.initials: PU
authors.lastname: Gilbert
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry* / Q000378:metabolism; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D004625:Embryo, Nonmammalian / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008854:Microscopy, Electron / Q000379:methods; D008903:Minerals / Q000737:chemistry / Q000378:metabolism; D044367:Phase Transition; D020133:Reverse Transcriptase Polymerase Chain Reaction; D047270:Strongylocentrotus purpuratus / Q000737:chemistry / Q000196:embryology / Q000378:metabolism; D014867:Water / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy / Q000379:methods
chemical_list: D001672:Biocompatible Materials; D016326:Extracellular Matrix Proteins; D008903:Minerals; C051691:SM50 protein, sea urchin; D014867:Water; D002119:Calcium Carbonate