ERC Advanced Investigator Grant Research Group at Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, Mainz D-55128, Germany.
FEBS Open Bio. 2013 Aug 16;3:357-62. doi: 10.1016/j.fob.2013.08.004. eCollection 2013.
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-μm 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 μm/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 °C), the pH value of the reaction assay (7.5/8.0), and the substrate concentration (CO2 and Ca(2+)). During the initial phase of crystallite formation, ≈40 μm 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 mM with respect to CaCO3. The deposits formed have a Martens hardness of ≈5 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.
针骨是钙质海绵的骨骼元素，其无机支架由碳酸钙（CaCO3）构成。直径约为 300 微米的针骨（如本研究中使用的钙质海绵 Sycon raphanus 的针骨）的生长是一个快速过程，速度约为 65 μm/h。碳酸钙的形成主要由碳酸酐酶（CA）完成。从海绵 S. raphanus 中分离并通过重组制备的酶。CA 驱动的 CaCO3 晶须沉积依赖于温度（最佳温度为 52°C）、反应测定的 pH 值（7.5/8.0）以及底物浓度（CO2 和 Ca（2+））。在晶核形成的初始阶段，形成约 40 μm 大的圆形沉积物，这些沉积物再重塑成较大的棱柱体。这些类晶体棱柱体相互连接，形成绳状/束状聚集体，或者沿着海绵针骨射线的相对表面完美排列，其较小的平面彼此平行。CA 依赖性 CaCO3 沉积可被 CA 特异性抑制剂乙酰唑胺抑制。CA 驱动的矿化的米氏常数（Michaelis-Menten constant）约为 8 mM（相对于 CaCO3）。形成的沉积物的马氏体硬度约为 5 GPa。这里呈现的数据首次强调了碳酸钙在海绵系统中的沉积是由酶决定的。这些数据将有助于开发适用于新型生物材料制造的新策略。
