mineralization front (Fig. 13.3d), newly formed minute nacre crystals have a typical
quadrangular shape and are oriented in the same direction. Proteolytic treatments
(Cuif et al. 1983a, b, 1985) revealed the ultrastructural organization of the nacre
crystallite and highlighted their composite nature. In particular, it showed that each
nacre crystallite is composed of minute granular elements (about 100 nm), which
may represent the basic mineral unit. For each tablet, it also showed a typical
pattern, characterized by the formation of opposite triangular domains of mineral
dissolution.
13.3.6 Minor Elements in Prisms and Nacre
Beside the shapes of their crystallites and their mineralogy, another aspect that
marks the difference between the prismatic and the nacreous layer is their bulk
elemental composition obtained by microprobe analysis (Masuda and Hirano 1980;
Cuif et al. 1985). Prisms exhibit high levels of magnesium and sulfur, respectively
6,000 and 4,000/4,500 ppm, while the concentrations of these two elements are
about 500 ppm in nacre. On the contrary, the concentrations of sodium and of
strontium are higher in nacre, respectively >6,000 and 1,500 ppm, in comparison to
prisms (4,500 and less than 1,000 ppm). The case of sulfur is interesting (Cuif et al.
1985, 1986, 1988a): its concentration, measured along the prisms, is constant
throughout the prisms length, but drastically collapses at the prisms/nacre transition. Few years ago, FTIR, WDX, and XANES data (Dauphin 2002; Dauphin 2003;
Dauphin et al. 2003) showed first that the sulfur in the prisms is present as sulfate,
and second, demonstrated that the intracrystalline prism matrix is particularly
enriched in sulfated polysaccharides. This corroborated the previous finding
of Wada (1980), who underlined the importance of sulfur (under the form of
polysaccharides) deposited on a glass coverslip preparation placed in Pinna
attenuata.
13.4 The Shell Matrices of Pinna sp. and of Pinna nobilis
13.4.1 Early Biochemical Studies
The discovery of “conchiolin”– the strongly insoluble organic fraction extracted
from nacre – and its subsequent naming by Fre ´my (1855) was the starting point of
the analysis of several insoluble organic fractions associated to diverse molluscan
shell microstructures. For almost a century, due to technical limitations, the biochemical information retrieved from shell proteins was circumscribed to that on the
composition in their elementary bricks, amino acids. Consequently, most of the
studies performed on shell matrices, between the beginning of the twentieth century
13 Acidic Shell Proteins of the Mediterranean Fan Mussel Pinna nobilis
367
quadrangular shape and are oriented in the same direction. Proteolytic treatments
(Cuif et al. 1983a, b, 1985) revealed the ultrastructural organization of the nacre
crystallite and highlighted their composite nature. In particular, it showed that each
nacre crystallite is composed of minute granular elements (about 100 nm), which
may represent the basic mineral unit. For each tablet, it also showed a typical
pattern, characterized by the formation of opposite triangular domains of mineral
dissolution.
13.3.6 Minor Elements in Prisms and Nacre
Beside the shapes of their crystallites and their mineralogy, another aspect that
marks the difference between the prismatic and the nacreous layer is their bulk
elemental composition obtained by microprobe analysis (Masuda and Hirano 1980;
Cuif et al. 1985). Prisms exhibit high levels of magnesium and sulfur, respectively
6,000 and 4,000/4,500 ppm, while the concentrations of these two elements are
about 500 ppm in nacre. On the contrary, the concentrations of sodium and of
strontium are higher in nacre, respectively >6,000 and 1,500 ppm, in comparison to
prisms (4,500 and less than 1,000 ppm). The case of sulfur is interesting (Cuif et al.
1985, 1986, 1988a): its concentration, measured along the prisms, is constant
throughout the prisms length, but drastically collapses at the prisms/nacre transition. Few years ago, FTIR, WDX, and XANES data (Dauphin 2002; Dauphin 2003;
Dauphin et al. 2003) showed first that the sulfur in the prisms is present as sulfate,
and second, demonstrated that the intracrystalline prism matrix is particularly
enriched in sulfated polysaccharides. This corroborated the previous finding
of Wada (1980), who underlined the importance of sulfur (under the form of
polysaccharides) deposited on a glass coverslip preparation placed in Pinna
attenuata.
13.4 The Shell Matrices of Pinna sp. and of Pinna nobilis
13.4.1 Early Biochemical Studies
The discovery of “conchiolin”– the strongly insoluble organic fraction extracted
from nacre – and its subsequent naming by Fre ´my (1855) was the starting point of
the analysis of several insoluble organic fractions associated to diverse molluscan
shell microstructures. For almost a century, due to technical limitations, the biochemical information retrieved from shell proteins was circumscribed to that on the
composition in their elementary bricks, amino acids. Consequently, most of the
studies performed on shell matrices, between the beginning of the twentieth century
13 Acidic Shell Proteins of the Mediterranean Fan Mussel Pinna nobilis
367