Interactions of sea-urchin skeleton macromolecules with growing calcite crystals- a study of intracrystalline proteins

A. Berman, L. Addadi, S. Weiner

Research output: Contribution to journalArticlepeer-review

446 Scopus citations


The exoskeletons of sea urchins are composed of magnesiumbearing calcite. Individual test plates and spines behave as single crystals in polarized light or when examined by X-ray diffraction1-3. They do not, however, cleave like inorganic calcite crystals along the {104} hexagonal cleavage planes, but have conchoidal fracture surfaces reminiscent of amorphous glass. Discussion of this paradox revolves around whether the phase is monocrystalline2,4,5, multicrystalline6, or some combination thereof7, but provides no explanation for the phenomenon. To address this question we grew crystals of calcite in the presence of acidic glycoproteins extracted from within the mineralized hard parts of sea-urchin tests8-10. As a control we used analogous proteins from the calcitic layer of a mollusc shell which are known to be nucleators of calcite when adsorbed on a rigid substrate, but inhibitors when in solution11-13. We show that the sea urchin, but not the mollusc macromolecules selectively adsorb onto specific calcite crystal planes and with continued crystal growth are occluded inside the solid phase. These synthetic crystals fracture with a conchoidal cleavage similar to that observed in sea-urchin calcite. Thus intracrystalline proteins may be responsible for this phenomenon in biology and the manner in which they affect the mechanical properties of the crystals may also have interesting implications to the materials sciences.

Original languageEnglish
Pages (from-to)546-548
Number of pages3
Issue number6156
StatePublished - 1 Jan 1988
Externally publishedYes

ASJC Scopus subject areas

  • General


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