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首页> 外文期刊>Biochemistry >NMR Studies of the Stability, Protonation States, and Tautomerism of 13C- and 15N-Labeled Aldimines of the Coenzyme Pyridoxal 5′-Phosphate in Water
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NMR Studies of the Stability, Protonation States, and Tautomerism of 13C- and 15N-Labeled Aldimines of the Coenzyme Pyridoxal 5′-Phosphate in Water

机译：水中13C和15N标记的辅酶Pyridoxal 5'-磷酸盐的Aldimines的稳定性，质子化状态和互变异构的NMR研究

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摘要

We have measured the pH-dependentn1nH,n13nC, and 15nN NMR spectra of pyridoxal 50n-phosphaten(n13nC2-PLP) mixed with equal amounts of either doubly 15nN-labeled diaminopropane,n15nNR-labeled L-lysine,norn15nNε-labeled L-lysine as model systems for various intermediates of the transimination reaction in PLP-ndependent enzymes.At low pH, only the hydrate and aldehyde forms of PLP and the free protonated diaminesnare present. Above pH 4, the formation of single- and double-headed aldimines (Schiff bases) with the addedndiamines is observed, and theirn13nC and 15nN NMR parameters have been characterized. For 1:1 mixtures thensingle-headed aldimines dominate. In a similarway, theNMRparameters of the geminal diamine formed withndiaminopropane at high pH are measured. However, no geminal diamine is formed with L-lysine. In contrastnto the aldimine formed with the ε-amino group of lysine, the aldimine formed with the R-amino group isnunstable at moderately high pH but dominates slightly below pH 10. By analyzing the NMR data, both thenmole fractions of the different PLP species and up to 6 different protonation states including their pKa valuesnwere obtained. Furthermore, the data show that all Schiff bases are subject to a proton tautomerismalong thenintramolecular OHN hydrogen bond, where the zwitterionic form is favored before deprotonation occurs atnhigh pH. This observation, as well as the observation that around pH7 the different PLP species are present inncomparable amounts, sheds new light on the mechanism of the transimination reaction.
机译：我们测量了吡ido醛50n-磷酸盐（n13nC2-PLP）与等量的双15nN标记的二氨基丙烷，n15nNR标记的L-赖氨酸，norn15nNε标记的L-赖氨酸混合的pH依赖性n1nH，n13nC和15nN NMR光谱在不依赖PLP的酶中进行转氨反应的各种中间体的模型系统。在低pH值下，仅存在PLP的水合物和醛形式以及游离的质子化二胺。在pH高于4的情况下，观察到形成了带有加成二胺的单头和双头醛亚胺（席夫碱），并表征了它们的n13nC和15nN NMR参数。对于1：1混合物，单头的亚胺占主导地位。以类似的方式，测量在高pH下与正二氨基丙烷形成的双链双胺的NMR参数。但是，L-赖氨酸不会形成双双胺。与由赖氨酸的ε-氨基形成的醛亚胺形成对比，由R-氨基形成的醛亚胺在中等较高的pH值下不稳定，但在pH值低于10时占优势。通过分析NMR数据，不同PLP物种的纳米级和获得多达6个不同的质子化状态，包括其pKa值。此外，数据表明，所有席夫碱都具有质子互变异构，然后是分子内的OHN氢键，其中两性离子形式在高质子化之前在去质子化之前是有利的。这一观察结果以及在pH7左右存在不同PLP物质数量无与伦比的观察结果为转氨反应的机理提供了新的思路。

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