在葡萄糖嵌入的野生型细菌视紫红质中，可以鉴定出M中间体的两种渐进底物。
Two progressive substrates of the M-intermediate can be identified in glucose-embedded, wild-type bacteriorhodopsin.
作者信息
Vonck J, Han B G, Burkard F, Perkins G A, Glaeser R M
机构信息
Life Sciences Division, Donner Laboratory, Lawrence Berkeley Laboratory, Berkeley, California 94720.
出版信息
Biophys J. 1994 Sep;67(3):1173-8. doi: 10.1016/S0006-3495(94)80585-5.
Glucose-embedded bacteriorhodopsin shows M-intermediates with different Amide I infrared bands when samples are illuminated at 240 or 260 K, in contrast with fully hydrated samples where a single M-intermediate is formed at all temperatures. In hydrated, but not in glucose-embedded specimens, the N intermediate is formed together with M at 260 K. Both Fourier transform infrared and electron diffraction data from glucose-embedded bacteriorhodopsin suggest that at 260 K a mixture is formed of the M-state that is trapped at 240 K, and a different M-intermediate (MN) that is also formed by mutant forms of bacteriorhodopsin that lack a carboxyl group at the 96 position, necessary for the M to N transition. The fact that an MN species is trapped in glucose-embedded, wild-type bacteriorhodopsin suggests that the glucose samples lack functionally important water molecules that are needed for the proton transfer aspartate 96 to the Schiff base (and, thus, to form the N-intermediate); thus, aspartate 96 is rendered ineffective as a proton donor.
当样品在240K或260K光照时，嵌入葡萄糖的细菌视紫红质显示出具有不同酰胺I红外波段的M中间体，这与完全水合的样品形成对比，在完全水合的样品中，在所有温度下都只形成单一的M中间体。在水合但非嵌入葡萄糖的标本中，N中间体在260K时与M一起形成。来自嵌入葡萄糖的细菌视紫红质的傅里叶变换红外和电子衍射数据均表明，在260K时形成了一种混合物，其中包括在240K时捕获的M态以及另一种不同的M中间体（MN），后者也由细菌视紫红质的突变形式形成，这些突变形式在96位缺少羧基，而该羧基对于M向N的转变是必需的。在嵌入葡萄糖的野生型细菌视紫红质中捕获了MN物种这一事实表明，葡萄糖样品缺少质子从天冬氨酸96转移至席夫碱（从而形成N中间体）所需的功能重要水分子；因此，天冬氨酸96作为质子供体变得无效。
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