1H Dynamic Nuclear Polarization Based on an Endogenous Radical

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• 作者：Thorsten Maly ; Dongtao Cui ; Robert G. Griffin ; Anne-Frances Miller
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：June 21, 2012
• 年：2012
• 卷：116
• 期：24
• 页码：7055-7065
• 全文大小：437K
• 年卷期：v.116,no.24(June 21, 2012)
• ISSN：1520-5207

文摘

We demonstrate a 15-fold enhancement of solid-state NMR signals via dynamic nuclear polarization (DNP) based on a stable, naturally occurring radical in a protein: the flavin mononucleotide (FMN) semiquinone of flavodoxin. The line width of flavodoxin鈥檚 EPR signal suggests that the dominant DNP mechanism is the solid effect, consistent with the field-dependent DNP enhancement profile. The magnitude of the enhancement as well as the bulk-polarization build-up time constant (蟿_B) with which it develops are dependent on the isotopic composition of the protein. Deuteration of the protein to 85% increased the nuclear longitudinal relaxation time T_1n and 蟿_B by factors of five and seven, respectively. Slowed dissipation of polarization can explain the 2-fold higher maximal enhancement than that obtained in proteated protein, based on the endogenous semiquinone. In contrast, the long 蟿_B of TOTAPOL-based DNP in nonglassy samples was not accompanied by a similarly important long T_1n, and in this case the enhancement was greatly reduced. The low concentrations of radicals occurring naturally in biological systems limit the magnitude of DNP enhancement that is attainable by this means. However, our enhancement factors of up to 15 can nonetheless make an important difference to the feasibility of applying solid-state NMR to biochemical systems. We speculate that DNP based on endogenous radicals may facilitate MAS NMR characterization of biochemical complexes and even organelles, and could also serve as a source of additional structural and physiological information.