A common property of biominerals is the presence of an organic fraction,
called organic matrix, intimately bound to the skeletal structure.
This matrix is not an incorporation of coral tissue but a controlled secretion
of specific molecules.
In invertebrate exoskeletons, two distinct organic fractions, one soluble
and one insoluble, are arbitrarily defined during their aqueous extraction.
To extract organic molecules from mineral, the mineral needs to be dissolved,
indicating a very close association between the crystals and the organic
molecules. In fact, following partial dissolution of a mollusc shell,
the organic matrix appears as a network surrounding the crystal and visible
to the interior of the crystal, suggesting its controlling action during
formation.
At the CSM, studies were made on aspartic acid incorporation in tissue
proteins, followed by the appearance of labelled macromolecules in the
skeleton. Incorporation within the skeleton of radiolabelled aspartic
acid is made with organic molecules and not with CaCO3
as was shown by preliminary experiments carried out in the laboratory.
The work is at present oriented towards determining the origin of the
organic matrix components and the regulating factors.
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