Moonen C T, Vervoort J, Müller F
Biochemistry. 1984 Oct 9;23(21):4868-72. doi: 10.1021/bi00316a008.
Several flavin model compounds in the reduced state have been investigated by 13C NMR techniques. The NMR spectra were recorded in dependence of temperature, in the range of 30 to -100 degrees C. The results show that the activation barrier for the ring inversion ("butterfly" motion) is too low to be observed directly. In order to be able to detect the barrier of the ring inversion, it was coupled with a side-chain rotation. In this way, the intrinsic barrier for the ring inversion is increased by the barrier of the side-chain rotation, which allowed detection of the former barrier. It is shown that the intrinsic barrier for the ring inversion is less than 20 kJ/mol. Moreover, it is shown that previous results of Tauscher et al. [Tauscher, L., Ghisla, S., & Hemmerich, P. (1973) Helv. Chim. Acta 56, 630-649] are incorrect and nitrogen inversion is not observed. Symmetry arguments in the dynamic processes are discussed. From the low activation barrier for the ring inversion, it can be concluded that the conformation of the reduced flavin can be easily influenced upon binding to apoflavoproteins. This aspect might be of importance in the regulation of the function of the flavin prosthetic group in biological systems.
已通过13C NMR技术研究了几种处于还原态的黄素模型化合物。NMR谱是在30至 -100摄氏度范围内随温度记录的。结果表明，环反转（“蝴蝶”运动）的活化能垒太低，无法直接观测到。为了能够检测环反转的能垒，将其与侧链旋转耦合。通过这种方式，环反转的固有能垒因侧链旋转的能垒而增加，从而使得能够检测到前者的能垒。结果表明，环反转的固有能垒小于20 kJ/mol。此外，结果表明Tauscher等人 [Tauscher, L., Ghisla, S., & Hemmerich, P. (1973) Helv. Chim. Acta 56, 630 - 649] 先前的结果是错误的，未观察到氮反转。讨论了动态过程中的对称论点。从环反转的低活化能垒可以得出结论，还原态黄素的构象在与脱辅基黄素蛋白结合时很容易受到影响。这一方面在生物系统中黄素辅基功能的调节中可能很重要。
