Paleonews

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2008-11-03 – Biomineralizzazione: la sintesi del Magnesio in biostrutture Mg-calcitiche (biomineralization)

Un team internazionale ha individuato un peptide idrofilo responsabile dell’inserzione di parti di manganese in “biocostruzioni” calcitiche (es.: ossa, conchiglie). Ciò è importante sia dal punto di vista “bio-tecnologico” in quanto spesso sono proprio le “impurità” a dare a un tessuto, biologico o meno, determinate caratteristihe; sia da un punto di vista paleontologico visto che gli organismi con guscio calcitico-magnesiaco (es. brachiopodi) sono usati come “paleo-termometri”.

Bare bones of crystal growth:

Biomolecules enhance metal contents in calcite

Blacksburg, Va. – From shells to bones, the skeletons of organisms contain small amounts of impurity elements such as magnesium. Because the levels of these elements provide important clues to past environments, a considerable effort has focused on understanding how to relate impurity contents to the ancient environments in which an organism lived.

In the October 31 issue of Science magazine, Allison Stephenson, a Ph.D. candidate in geoscience, and Patricia Dove, professor of geoscience in the College of Science at Virginia Tech, and colleagues* report that a hydrophilic peptide, similar in character to those found in calcifying organisms, significantly enhances the magnesium (Mg)-content of calcite.

“We knew from another study in our group (Elhadj et al., 2006, PNAS) that the chemistry of simple peptides as well as proteins could be tuned to control crystal growth rate and change crystal morphology,” said Dove. “From that understanding, we realized that the water-structuring abilities of certain biomolecules could also influence the amount of impurities that can go into minerals.”

“All organisms use proteins to grow minerals into complex shapes with remarkable functions,” said lead author Stephenson. “But this finding is especially meaningful for geologists because Mg-content in carbonates is used as a ‘paleo thermometer’. That is, we know that Mg content increases with temperature, but now we see that certain biomolecules could also affect those ‘signatures’. The findings raise questions about the interplay of different factors on metal-contents in biominerals.”

The findings also offer new insights for materials synthesis because a high degree of control on impurities is often necessary to give specific properties such as strength or electrical conductivity. By using biomolecules, it may be possible to tune impurities to desired levels, Dove said.

“Also, this basic research suggests new ways of looking at biochemical origins of pathological skeletal mineralization, and whether local biochemistry could influence the uptake of toxic metals into human skeletons,” Stephenson said.

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 *The article (http://www.sciencemag.org/cgi/content/short/322/5902/724), “Peptides enhance magnesium signature in calcite: Insights into origins of vital effects,” was written by Stephenson; J. J. DeYoreo of the Chemistry and Materials Science Directorate, Lawrence Livermore National Lab (LLNL), Dove’s former student; L. Wu of LLNL and the Department of Applied Science, University of California–Davis; K. J. Wu of LLNL; J. Hoyer of the Department of Biological Sciences, University of Delaware; and Dove. See also related work just published in Nature which cites this article: http://www.nature.com/news/2008/081030/full/news.2008.1197.html

The paper is part of Dove’s ongoing research into mineral nucleation, growth, and dissolution, aimed towards understanding processes of biomineralization, cementation, global elemental cycling, and climate proxy models. Her research group mimics processes from both biological and inorganic settings to understand underlying reaction mechanisms through direct, nanoscale measurements of mineral-water interactions and their kinetic and surface thermodynamic properties.

Research in Dove’s group is supported by the DOE Basic Energy Sciences, the NSF EAR program in Geobiology and Environmental Geochemistry, and the NSF OCE program in Chemical Oceanography. For more information, visit Biogeochemistry of Earth Processes website: www.geochem.geos.vt.edu/bgep/

Contact: Susan Trulove – STrulove@vt.edu – 540-231-5646 – Virginia Tech

source: http://www.eurekalert.org/pub_releases/2008-10/vt-bbo103108.php

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Peptides Enhance Magnesium Signature in Calcite: Insights into Origins of Vital Effects

A. E. Stephenson,1* J. J. DeYoreo,2 L. Wu,2,3 K. J. Wu,2 J. Hoyer,4 P. M. Dove1*

Science 31 October 2008:
Vol. 322. no. 5902, pp. 724 – 727
DOI: 10.1126/science.1159417

Abstract: Studies relating the magnesium (Mg) content of calcified skeletons to temperature often report unexplained deviations from the signature expected for inorganically grown calcite. These “vital effects” are believed to have biological origins, but mechanistic bases for measured offsets remain unclear. We show that a simple hydrophilic peptide, with the same carboxyl-rich character as that of macromolecules isolated from sites of calcification, increases calcite Mg content by up to 3 mole percent. Comparisons to previous studies correlating Mg content of carbonate minerals with temperature show that the Mg enhancement due to peptides results in offsets equivalent to 7° to 14°C. The insights also provide a physical basis for anecdotal evidence that organic chemistry modulates the mineralization of inorganic carbonates and suggest an approach to tuning impurity levels in controlled materials synthesis.

correspondence should be addressed. E-mail: dove@vt.edu (P.M.D.) and aestephe@vt.edu (A.E.S.)

novembre 3, 2008 - Posted by | Articolo sc. di riferimento, Italiano (riassunto), Paleontology / Paleontologia | , ,

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