Carbonic anhydrase (CA), an enzyme that catalyzes the carbon dioxide (CO₂) hydration, has been suggested as a potentially powerful agent for CO₂ capture and utilization. For successful application, CA should withstand the harsh environment presented by CO₂-capturing facilities. While there have been intensive efforts to identify and engineer thermostable CAs, other required conditions such as the high salt concentration of CO₂ absorbents have often been ignored. Herein, we expressed, purified, and characterized a novel α-type CA (hmCA) possessing an unusual N-terminal extension from the halophilic marine bacterium Hydrogenovibrio marinus. We found that the N-terminal extension strongly influenced the enzyme solubility. Recombinant hmCA showed catalytic efficiency comparable to other bacterial α-type CAs. hmCA was less inhibited by anionic inhibitors showing 1.6- (NO₃⁻), 3.1- (NO₂⁻), and 3.7-fold (Cl⁻) higher inhibition constants than those of mesophilic bovine CA (bCA), suggesting halotolerance. Recombinant hmCA was markedly stabilized using most of the alkali metal salts tested, showing 19 °C higher melting temperature at 1 M NaCl compared to bCA that was significantly destabilized. The region of N-terminal extension seemed not to be involved in halotolerance. The remarkable halotolerance may be attributed to the uneven distribution of electrostatic potential and the localized negative charge on the hmCA surface. hmCA displayed ∼29-fold longer half-life than that of bCA at 40 °C in potassium carbonate as a practical absorbent, suggesting that halotolerance should be considered another key characteristic in the development of biocatalysts for CO₂ capture using high-salt-containing CO₂ absorbents.

碳酸酐酶（CA）是一种催化二氧化碳（CO ₂）水合的酶，已被认为是潜在的强大的CO ₂捕获和利用剂。为了成功应用，CA应该承受由CO ₂捕获设施带来的恶劣环境。尽管已经进行了大量的努力来识别和设计热稳定的CA，但是其他要求的条件（例如高盐浓度的CO ₂吸收剂）常常被忽略。在这里，我们表达，纯化和表征了新型的α型CA（hm CA），其具有从嗜盐海洋细菌Hydrogenovibrio marinus的不寻常的N端延伸。我们发现，N-末端延伸强烈影响酶的溶解度。重组hm CA的催化效率可与其他细菌α型CA媲美。HM CA被以下通过示出1.6-（NO阴离子抑制剂来抑制₃ ^-，3.1-（NO）₂ ^{- ），}和3.7倍（CL ^- ）更高的抑制常数比嗜温牛CA（BCA），提示耐盐。重组hm使用大多数测试的碱金属盐，CA可以显着稳定，与明显不稳定的bCA相比，在1 M NaCl下熔融温度显示高19°C。N端延伸区似乎不参与耐盐性。显着的耐光性可归因于静电势的不均匀分布和hm CA表面上的局部负电荷。作为一种实用的吸收剂，在40°C的碳酸钾中，hm CA的半衰期比bCA的半衰期长约29倍，这表明耐盐性应被认为是开发使用高盐分CO2捕集CO ₂的生物催化剂的另一个关键特性。含有CO ₂吸收剂。