Shitov Alexandr V, Terentyev Vasily V, Govindjee Govindjee
Institute of Basic Biological Problems, Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Institutskaya Street 2, Moscow Region, 142290, Pushchino, Russia.
Department of Biochemistry, Department of Plant Biology, and Center of Biophysics & Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
Plant Physiol Biochem. 2025 Apr;221:109516. doi: 10.1016/j.plaphy.2025.109516. Epub 2025 Jan 18.
Carbonic anhydrase (CA) activity, associated with Photosystem II (PSII), has been shown to enhance water oxidation. However, CA activity was thought to be a side effect or even a "contamination" of other CAs because of the relatively low rates of CA reactions in PSII measured previously. Here, by using 8-hydroxy-pyrene-1,3,6-trisulfonate (pyranine), a fluorescent dye, as a pH indicator, we show that PSII preparations (∗∗BBYs) from Pisum sativum have a high CA activity (as measured by HCO dehydration), which is close to that of highly active CAs. This fluorescence method is new for BBYs giving at least ten times higher activity than the other methods used earlier, as well as being highly sensitive and, thus, more convenient to use for BBYs than any other approach. We show here that the pH range of 5.0-7.5 is optimum for the pyranine measuring system, in general, and this pH range is suitable not only for the CA in BBYs but also for other CAs. Further, the CA activity of BBYs has the following unique properties: (1) low sensitivity to some known, and otherwise, effective CA inhibitors; (2) an opposite pH profile of HCO dehydration than observed in other known CAs. These findings indicate that the high CA activity, we have observed, belongs to BBYs, i.e., free of other CAs. At pH 6.5, CA activity of BBYs is shown to be directly correlated with that of photosynthetic O evolution. We propose that the CA activity may accelerate the removal of Hs during water oxidation. # Celebrating 80th birthday of Alan James Stemler, a pioneer on the role of bicarbonate on the electron donor side of Photosystem II. S.G. Vaklinova & associates (1982), and A.J. Stemler (1986) were the first who have measured carbonic anhydrase activity in Photosystem II preparations. ∗∗ BBYs stand for Photosystem II samples made by the procedure of Berthold (B), Babcock (B) and Yocum (Y); see Berthold et al. (1981).
与光系统II（PSII）相关的碳酸酐酶（CA）活性已被证明可增强水的氧化。然而，由于之前测得的PSII中CA反应速率相对较低，CA活性被认为是其他碳酸酐酶的副作用甚至是一种“污染”。在这里，我们使用荧光染料8-羟基芘-1,3,6-三磺酸盐（吡喃荧光素）作为pH指示剂，发现豌豆的PSII制剂（BBYs）具有较高的CA活性（通过HCO脱水测定），这与高活性碳酸酐酶的活性相近。这种荧光方法对于BBYs来说是新的，其活性比早期使用的其他方法至少高十倍，而且高度灵敏，因此比任何其他方法都更便于用于BBYs。我们在此表明，一般来说，5.0 - 7.5的pH范围对于吡喃荧光素测量系统是最佳的，这个pH范围不仅适用于BBYs中的CA，也适用于其他碳酸酐酶。此外，BBYs的CA活性具有以下独特性质：（1）对一些已知的且在其他情况下有效的CA抑制剂不敏感；（2）HCO脱水的pH曲线与其他已知碳酸酐酶相反。这些发现表明，我们观察到的高CA活性属于BBYs，即不含其他碳酸酐酶。在pH 6.5时，BBYs的CA活性与光合放氧活性直接相关。我们提出，CA活性可能在水氧化过程中加速H⁺的去除。# 庆祝艾伦·詹姆斯·施特勒80岁生日，他是研究碳酸氢盐在光系统II电子供体侧作用的先驱。S.G. 瓦克林诺娃及其同事（1982年）和A.J. 施特勒（1986年）是最早测量光系统II制剂中碳酸酐酶活性的人。**BBYs代表通过贝托尔德（B）、巴布科克（B）和约库姆（Y）的方法制备的光系统II样品；见贝托尔德等人（1981年）。
