✍ Scribed by Subramanyam Gayathri; Rajamani Lakshminarayanan; James C. Weaver; Daniel E. Morse; R. Manjunatha Kini; Suresh Valiyaveettil
No coin nor oath required. For personal study only.
The mechanisms of formation of biogenic magnesium‐rich calcite remain an enigma. Here we present ultrastructural and compositional details of ossicles from the seastar Pisaster giganteus (Echinodermata, Asteroidea). Powder X‐ray diffraction, infrared spectroscopy and elemental analyses confirm that the ossicles are composed of magnesium‐rich calcite, whilst also containing about 0.01 % (w/w) of soluble organic matrix (SOM) as an intracrystalline component. Amino acid analysis and N‐terminal sequencing revealed that this mixture of intracrystalline macromolecules consists predominantly of glycine‐rich polypeptides. In vitro calcium carbonate precipitation experiments indicate that the SOM accelerates the conversion of amorphous calcium carbonate (ACC) into its final crystalline product. From this observation and from the discovery of ACC in other closely related taxa, it is suggested that substitution of magnesium into the calcite lattice through a transient precursor phase may be a universal phenomenon prevalent across the phylum echinodermata.
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The application of a new type of intracellular magnesium-selective microelectrode based on the neutral carrier ETH5214 to measure intracellular free magnesium ([Mg]i) in frog skeletal muscle fibers is reported. At room temperature (18-20~ the average values for [Mg]i was 0.93 mmol/1 (pMg~ = 3.03 • 0