We developed an effective fluorometric technique to quantify extracellular carbonic anhydrase (eCA) present in natural seawater samples. The technique includes the separation of eCA from cells to achieve low detection limits through high signal : noise ratios. eCA was efficiently extracted from cell membranes by treatment with 0.1 M phosphate buffer containing 2.5 M NaCl. The free eCA specifically forms a fluorescent complex with dansylamide, and the detection limit of the complex is below 0.1 nM. We applied the technique to samples from different culture solutions and natural seawater collected from the Baltic Sea. We observed eCA concentrations to be in the range of 0.10-0.67 nM in natural seawater. The data indicated that this technique is very sensitive, accurate, and feasible for routine and shipboard measurement of eCA from natural seawater. It is therefore an effective and rapid tool to investigate the carbon acquisition of phytoplankton both in mono culture as well natural communities.

中文翻译：

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细胞外碳酸酐酶：方法开发及其在天然海水中的应用。

我们开发了一种有效的荧光技术来量化天然海水样品中存在的细胞外碳酸酐酶（eCA）。该技术包括将eCA与细胞分离，以通过高信噪比实现低检测限。通过用含有2.5 M NaCl的0.1 M磷酸盐缓冲液处理，可以有效地从细胞膜中提取eCA。游离的eCA可以与丹磺酰胺特异性地形成荧光配合物，并且该配合物的检测限低于0.1 nM。我们将该技术应用于来自不同养殖溶液的样品以及从波罗的海收集的天然海水。我们观察到天然海水中的eCA浓度在0.10-0.67 nM的范围内。数据表明，该技术对于常规和船上天然海水中eCA的测量非常灵敏，准确且可行。