Michel H, Schmidt W, Hemmerich P
Biophys Chem. 1982 May;15(2):121-30. doi: 10.1016/0301-4622(82)80024-0.
This paper continues the studies of vesicle-bound flavins ('anisotropic flavin chemistry'). It is possible to anchor the flavin nucleus in various modes within the lipids/water interface by means of long aliphatic chains and using different saturated lipids, thereby mimicking the specific binding of the coenzyme to the apoprotein in flavoproteins. Based on absorption spectroscopy and EPR spectroscopy studies we explored the rotational mobility and the microenvironment of membrane-bound amphiflavin radicals. N(5)-unsubstituted amphiflavin radicals exhibit a similarly high disproportionation constant as known from isotropic flavin chemistry. However, reasonable stabilization of the radical was achieved by introduction of an alkyl group in position 5 in the reduced state prior to the one-electron oxidation. Adopting the fine structure of the corresponding EPR spectra as assay for the mobility of the semiquinone, we determined rotational relaxation times ranging from 60 ns in the crystalline state down to 10 or 15 ns in the liquid-crystalline state of the membrane. The solvatochromic effect shown by absorption spectra of the membrane-bound flavin radicals reflects a dielectric constant of the microenvironment of c = 30-40, corresponding to the lipid/water interface region. The results obtained in this study are consistent with those obtained previously, from fluorescence analyses, supporting our former conclusions.
本文延续了对囊泡结合黄素（“各向异性黄素化学”）的研究。通过长脂肪链并使用不同的饱和脂质，有可能将黄素核以各种方式锚定在脂质/水界面内，从而模拟黄素蛋白中辅酶与脱辅基蛋白的特异性结合。基于吸收光谱和电子顺磁共振光谱研究，我们探究了膜结合两性黄素自由基的旋转流动性和微环境。N(5)-未取代的两性黄素自由基表现出与各向同性黄素化学中已知的类似高的歧化常数。然而，通过在单电子氧化之前在还原态的5位引入烷基，实现了自由基的合理稳定。采用相应电子顺磁共振光谱的精细结构作为半醌流动性的测定方法，我们测定了旋转弛豫时间，范围从晶体状态下的60纳秒到膜液晶状态下的10或15纳秒。膜结合黄素自由基吸收光谱显示的溶剂化显色效应反映了微环境的介电常数c = 30 - 40，对应于脂质/水界面区域。本研究获得的结果与先前通过荧光分析获得的结果一致，支持了我们之前的结论。
