Calcium biominerals 342

Fricke M, Volkmer D (2007) Crystallization of Calcium Carbonate Beneath Insoluble Mono-layers Suitable Models of Mineral-Matrix Interactions in Biomineralization 270 1-41 Fujimoto D, see Tamura R (2007) 269 53-82... 

Bone, shell, and coral are not, however, the only biominerals created by living organisms. The kidney and liver of animals, for example, often synthesize biominerals in the form of pathological stones (known as calculi) of varied composition (mostly of calcium oxalate, calcium phosphate, or... 

The bones and teeth of humans and other vertebrate animals, for example, consist mainly of a composite material made up of an organic substance, collagen, and a biomineral, calcium carbonate phosphate (see Textboxes 32 and 61). The latter, which makes up about two-thirds of the total dry weight of bone, is composed of calcium phosphate containing between 4-6% calcite (composed of calcium carbonate) as well as small amounts of sodium, magnesium, fluorine, and other trace elements. The formula Ca HPChXPChMCChXOH) approximately represents its composition its crystal structure is akin to that... 

Calcium 3.6 x 104 4.1 x lO-2 Second messenger, muscle activation, biominerals... 

As mentioned earlier, biological systems have developed optimized strategies to design materials with elaborate nanostructures [6]. A straightforward approach to obtaining nanoparticles with controlled size and organization should therefore rely on so-called biomimetic syntheses where one aims to reproduce in vitro the natural processes of biomineralization. In this context, a first possibility is to extract and analyze the biological (macro)-molecules that are involved in these processes and to use them as templates for the formation of the same materials. Such an approach has been widely developed for calcium carbonate biomimetic synthesis [13]. In the case of oxide nanomaterials, the most studied system so far is the silica shell formed by diatoms [14]. 

Ca2+ pumps are needed for the removal of calcium from cells, as in the maintenance of low Ca2+ levels in resting muscle, in bone deposition, and in biomineralization. The Na+/Ca2+ exchanger and Ca2+-ATPase (a Ca2+/H+-exchanger) act in parallel to pump Ca2+ across membranes, the latter being considerably more effective than the former. X-ray structure determinations have been carried out both for Ca2+-ATPase and for its Ca2+-bound form (443). The latter contains two Ca2+ ions... 

Calcium, a crucial second messenger signalling key changes in cellular metabolism, is also important in muscle activation, in the activation of many proteases, both intra- and extracellular, and as a major component of an range of biominerals, including bone. 

CALCIUM-BASED BIOMINERALS CALCIUM CARBONATES IN ASCIDIANS AND MOLLUSCS... 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Ca5(P04)30H]2, usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralization process leading to the hardest mineralized tissue known, the enamel of mammalian teeth. 

Finally, it is intriguing that in terms of biomineralization, invertebrates have based their reliance on calcium carbonates, while vertebrates appear to have used almost exclusively calcium phosphate. We say almost, because, while the use of calcium phosphates for biomineralization is an invention of some vertebrates, they still use calcium carbonate for the formation of otoliths4 of the inner ear. It remains to be established if the equivalent of the gene starmaker required for otolith formation in zebrafish has homologues among invertebrates. 

CALCIUM/CALMODULIN-DEPENDENT PROTEIN KINASE Calcium carbonate (CaCOs), BIOMINERALIZATION SOLUBILITY PRODUCT Calcium hydroxide (Ca(OH)2),... 

Monje, P. V., and Baran, E. J. (2002). Characterization of calcium oxalates generated as biominerals in cacti. Plant Physiol. 128, 707-713. 

Biomineralization, 36 137-139 calcium carbonate, 36 163-167 in algae, 36 166-167 gravity sensors, 36 164-166 carbonate/sulfate mineralization mechanisms, 36 171-175... 

Calcium carbide, 11 182-183 neutron diffraction studies on, 8 234 Calcium carbonate, biomineralization, 36 163-167... 

---