利用停流法测量α-羧酶体中碳酸酐酶的活性

4区 生物学 Q3 Biochemistry, Genetics and Molecular Biology
Methods in enzymology Pub Date : 2024-01-01 Epub Date: 2024-10-28 DOI:10.1016/bs.mie.2024.10.012
Nikoleta Vogiatzi, Cecilia Blikstad
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引用次数: 0

摘要

羧酶体是以蛋白质为基础的细胞器,是细菌二氧化碳浓缩机制(CCM)的核心。它们存在于所有蓝藻和许多化能自养蛋白细菌中,在蛋白质外壳内包裹着二氧化碳固定的关键酶--碳酸酐酶和羧化酶 Rubisco。CCM 在细胞质中积极积累碳酸氢盐,然后扩散到羧化酶体中,在那里碳酸酐酶迅速将碳酸氢盐平衡为二氧化碳。这就在 Rubisco 周围形成了高浓度的二氧化碳,确保了高效的羧化作用。在本章中,我们介绍了纯化α-羧酶体和测量这些纯化区室中碳酸酐酶活性的一般方法。我们以从化自养型卤代硫杆菌(Halothiobacillus neapolitanus c2)中纯化的α-羧酶体为例进行了说明,卤代硫杆菌是基于α-羧酶体的 CCM 的模式生物。不过,这种纯化方案也可适用于其他物种,如来自α-蓝藻的羧酶体或在异源宿主中表达的羧酶体。此外,我们还介绍了哈利法/pH 指示剂测定法,用于测量碳酸酐酶催化二氧化碳水合作用的稳态动力学。通过这种方法,我们可以确定纯化的 α 羧酶体的动力学参数 kcat、KM 和 kcat/KM。该方法使用停流光谱仪进行快速混合和检测,这对于捕捉二氧化碳和碳酸氢盐之间的快速平衡至关重要。由于质子释放,pH 指示剂会变色,通过吸光度监测反应进展。虽然该方法专门用于测量羧酶体上碳酸酐酶的活性,但也可用于测量其他环境中碳酸酐酶的活性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Measuring carbonic anhydrase activity in alpha-carboxysomes using stopped-flow.

Carboxysomes are protein-based organelles that serve as the centerpiece of the bacterial CO2 concentration mechanism (CCM). They are present in all cyanobacteria and many chemoautotrophic proteobacteria and encapsulate the key enzymes for CO2 fixation, carbonic anhydrase and the carboxylase Rubisco, within a protein shell. The CCM actively accumulates bicarbonate in the cytosol, which diffuses into the carboxysome where carbonic anhydrase rapidly equilibrates it to CO2. This creates a high CO2 concentration around Rubisco, ensuring efficient carboxylation. In this chapter, we present a general method for purifying α-carboxysomes and measuring carbonic anhydrase activity within these purified compartments. We exemplify this with α-carboxysomes purified from the chemoautotroph Halothiobacillus neapolitanus c2, a model organism for the α-carboxysome based CCM. However, this purification protocol can be adapted for other species, such as carboxysomes from α-cyanobacteria or carboxysomes expressed in heterologous hosts. Further, we describe the Khalifah/pH indicator assay for measuring steady-state kinetics of carbonic anhydrase catalyzed CO2 hydration. This method allows us to determine the kinetic parameters kcat, KM and kcat/KM for the purified α-carboxysomes. It uses a stopped-flow spectrometer for rapid mixing and detection, crucial for capturing the fast equilibrium between CO2 and bicarbonate. The reaction progress is monitored by absorbance via a pH indicator that changes color due to the proton release. While the method specifically focuses on measuring carbonic anhydrase activity on carboxysomes, it can be used to measure activity on carbonic anhydrases from other contexts as well.

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来源期刊
Methods in enzymology
Methods in enzymology 生物-生化研究方法
CiteScore
2.90
自引率
0.00%
发文量
308
审稿时长
3-6 weeks
期刊介绍: The critically acclaimed laboratory standard for almost 50 years, Methods in Enzymology is one of the most highly respected publications in the field of biochemistry. Each volume is eagerly awaited, frequently consulted, and praised by researchers and reviewers alike. Now with over 500 volumes the series contains much material still relevant today and is truly an essential publication for researchers in all fields of life sciences, including microbiology, biochemistry, cancer research and genetics-just to name a few. Five of the 2013 Nobel Laureates have edited or contributed to volumes of MIE.
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