Polymorphic carbonate in fish otoliths

Many organisms exhibit astonishing biomineralization abilities, forming polymorphic minerals from the same chemical substance. Fish inner ear otoliths consist of calcium carbonate (CaCO₃) in various polymorphic forms (e.g., vaterite, aragonite). Proteins are known to be involved in controlling polymorphic forms, with a new study suggesting a mechanism involving phosphorylation of a protein responsible of biomineralisation. Phosphorylation corresponds to calcium carbonate crystallizing as vaterite, whereas its absence leads to calcite precipitation.

Figure: An experiment suggesting different biomineralization activity of a Starmaker-like protein (from fish otoliths), which in its phosphorylated form influences the formation of vaterite, whereas it promotes the formation of calcitic calcium carbonate crystals if it is in a dephosphorylated form.