The enzyme carbonic anhydrase as an integral component of biogenic Ca-carbonate formation in sponge spicules

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• 作者：Werner E.G. M眉ller ; Heinz C. Schr枚der ; Ute Schlossmacher ; Meik Neufurth ; Werner Geurtsen ; Michael Korzhev ; Xiaohong Wang
• 关键词：Sponge ; Calcareous spicules ; Carbonic anhydrase ; Crystal formation ; Sycon raphanus
• 刊名：FEBS Open Bio
• 出版年：2013
• 年：2013
• 卷：3
• 期：Complete
• 页码：357-362
• 全文大小：1139 K

文摘

The inorganic scaffold of the spicules, the skeletal elements of the calcareous sponges, is formed of calcium carbonate (CaCO₃). The growth of the approximately 300-渭m large spicules, such as those of the calcareous sponge Sycon raphanus used in the present study, is a rapid process with a rate of about 65聽渭m/h. The formation of CaCO₃ is predominantly carried out by the enzyme carbonic anhydrase (CA). The enzyme from the sponge S. raphanus was isolated and prepared by recombination. The CA-driven deposition of CaCO₃ crystallites is dependent on temperature (optimal at 52 掳C), the pH value of the reaction assay (7.5/8.0), and the substrate concentration (CO₂ and Ca²⁺). During the initial phase of crystallite formation, 鈮?0聽渭m large round-shaped deposits are formed that remodel to larger prisms. These crystal-like prisms associate to each other and form either rope-/bundle-like aggregates or arrange perfectly with their smaller planes along opposing surfaces of the sponge spicule rays. The CA-dependent CaCO₃ deposition can be inhibited by the CA-specific inhibitor acetazolamide. The Michaelis-Menten constant for the CA-driven mineralization has been determined to be around 8聽mM with respect to CaCO₃. The deposits formed have a Martens hardness of 鈮?聽GPa. The data presented here highlights for the first time that calcite deposition in the sponge system is decisively controlled enzymatically. This data will contribute to the development of new strategies applicable for the fabrication of novel biomaterials.