Hovan Andrej, Sedláková Dagmar, Lee One-Sun, Bánó Gregor, Sedlák Erik
Department of Biophysics, Faculty of Science, P. J. Šafárik University in Košice Jesenná 5 041 54 Košice Slovakia.
Department of Biophysics, Institute of Experimental Physics, Slovak Academy of Sciences Watsonova 47 040 01 Košice Slovakia.
RSC Adv. 2024 Sep 11;14(39):28783-28790. doi: 10.1039/d4ra05540c. eCollection 2024 Sep 4.
Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are frequently used interchangeably in the catalysis of various reactions as part of flavoenzymes because they have the same functional component, the isoalloxazine ring. However, they differ significantly in their conformational properties. The inclusion of two planar rings in the structure of FAD greatly increases the range of possible conformations compared to FMN. An exemplary instance of this is the remarkable disparity in singlet oxygen efficiency production, , between FMN and FAD. Under neutral pH conditions, FAD has low photosensitizing activity with ∼ 0.07 while FMN demonstrates high photosensitizing activity with ∼ 0.6. Both adenine rings and isoalloxazine in FAD contain pH titratable groups. Through comprehensive analysis of the kinetics of the transient absorbance of the triplet state and the phosphorescence of singlet oxygen from FAD and FMN, we determined the correlation between different conformational states and the pH-dependent generation of singlet oxygen. Based on our findings, we may deduce that within the pH range of pH 2 to pH 13, only two out of the five potential structural states of FAD are capable of efficiently producing singlet oxygen. There are two open conformations: (i) an acidic FAD conformation with a protonated adenine ring, which is around 10 times more populated than the neutral open FAD conformation, and (ii) a neutral pH FAD conformation, which is significantly less populated. The FAD conformer with a protonated adenine ring at acidic pH generates singlet oxygen with approximately 50% efficiency compared to the constantly open FMN at neutral pH. This may have implications for singlet oxygen synthesis in acidic environments.
黄素腺嘌呤二核苷酸（FAD）和黄素单核苷酸（FMN）作为黄素酶的一部分，在各种反应的催化过程中经常被互换使用，因为它们具有相同的功能成分——异咯嗪环。然而，它们的构象性质存在显著差异。与FMN相比，FAD结构中包含两个平面环，这大大增加了可能的构象范围。一个典型的例子是FMN和FAD在单线态氧产生效率 方面存在显著差异。在中性pH条件下，FAD的光敏活性较低， 约为0.07，而FMN则表现出较高的光敏活性， 约为0.6。FAD中的腺嘌呤环和异咯嗪都含有可进行pH滴定的基团。通过对FAD和FMN三线态瞬态吸收动力学以及单线态氧磷光的综合分析，我们确定了不同构象状态与单线态氧pH依赖性生成之间的相关性。基于我们的研究结果，可以推断在pH 2至pH 13的范围内，FAD的五种潜在结构状态中只有两种能够有效地产生单线态氧。有两种开放构象：（i）一种酸性FAD构象，其腺嘌呤环质子化，其数量比中性开放FAD构象多约10倍；（ii）一种中性pH的FAD构象，其数量明显较少。在酸性pH下腺嘌呤环质子化的FAD构象产生单线态氧的效率约为中性pH下持续开放的FMN的50%。这可能对酸性环境中的单线态氧合成有影响。
