Allen J P, Artz K, Lin X, Williams J C, Ivancich A, Albouy D, Mattioli T A, Fetsch A, Kuhn M, Lubitz W
Department of Chemistry and Biochemistry, Arizona State University, Tempe 85287-1604, USA.
Biochemistry. 1996 May 28;35(21):6612-9. doi: 10.1021/bi9528311.
The properties of the primary electron donor in reaction centers from Rhodobacter sphaeroides have been investigated in mutants containing a bacteriochlorophyll (BChl)--bacteriopheophytin (BPhe) dimer with and without hydrogen bonds to the conjugated carbonyl groups. The heterodimer mutation His M202 to Leu was combined with each of the following mutations: His L168 to Phe, which should remove an existing hydrogen bond to the BChl molecule; Leu L131 to His, which should add a hydrogen bond to the BChl molecule; and Leu M160 to His and Phe M197 to His, each of which should add a hydrogen bond to the BPhe molecule [Rautter, J., Lendzian, F., Schulz, C., Fetsch, A., Kuhn M., Lin, X., Williams, J. C., Allen J. P., & Lubitz, W. (1995) Biochemistry 34, 8130-8143]. Pigment extractions and Fourier transform Raman spectra confirm that all of the mutants contain a heterodimer. The bands in the resonance Raman spectra arising from the BPhe molecule, which is selectively enhanced, exhibit the shifts expected for the addition of a hydrogen bond to the 9-keto and 2-acetyl carbonyl groups. The oxidation--reduction midpoint potential of the donor is increased by approximately 85 mV by the addition of a hydrogen bond to the BChl molecule but is only increased by approximately 15 mV by the addition of a hydrogen bond to the BPhe molecule. An increase in the rate of charge recombination from the primary quinone is correlated with an increase in the midpoint potential. The yield of electron transfer to the primary quinone is 5-fold reduced for the mutants with a hydrogen bond to the BPhe molecule. Room- and low-temperature optical absorption spectra show small differences from the features that are typical for the heterodimer, except that a large increase in absorption is observed around 860-900 nm for the donor Qy band in the mutant that adds a hydrogen bond to the BChl molecule. The changes in the optical spectra and the yield of electron transfer are consistent with a model in which the addition of a hydrogen bond to the BChl molecule increases the energy of an internal charge transfer state while the addition to the BPhe molecule stabilizes this state. The results show that the properties of the heterodimer are different depending on which side is hydrogen-bonded and suggest that the hydrogen bonds alter the energy of the internal charge transfer state in a well-defined manner.
在球形红细菌反应中心的初级电子供体特性研究中，针对含有细菌叶绿素（BChl）-细菌脱镁叶绿素（BPhe）二聚体且与共轭羰基有或没有氢键的突变体进行了研究。异二聚体突变His M202突变为Leu，并与以下每个突变组合：His L168突变为Phe，这应消除与BChl分子现有的氢键；Leu L131突变为His，这应添加一个与BChl分子的氢键；Leu M160突变为His以及Phe M197突变为His，每个突变都应添加一个与BPhe分子的氢键[劳特，J.，伦齐安，F.，舒尔茨，C.，费奇，A.，库恩，M.，林，X.，威廉姆斯，J.C.，艾伦，J.P.，&卢比茨，W.（1995年）《生物化学》34卷，8130 - 8143页]。色素提取和傅里叶变换拉曼光谱证实所有突变体都含有异二聚体。共振拉曼光谱中由被选择性增强的BPhe分子产生的谱带，呈现出向9 - 酮基和2 - 乙酰羰基添加氢键时预期的位移。通过向BChl分子添加氢键，供体的氧化还原中点电位增加约85 mV，但通过向BPhe分子添加氢键仅增加约15 mV。从初级醌进行电荷复合的速率增加与中点电位的增加相关。对于与BPhe分子有氢键的突变体，向初级醌的电子转移产率降低了5倍。室温及低温光吸收光谱与异二聚体的典型特征有微小差异，只是在向BChl分子添加氢键的突变体中，供体Qy带在860 - 900 nm附近观察到吸收大幅增加。光谱变化和电子转移产率与一个模型一致，即向BChl分子添加氢键会增加内部电荷转移态的能量，而向BPhe分子添加氢键会稳定该状态。结果表明，异二聚体的特性取决于哪一侧形成氢键，并表明氢键以明确的方式改变内部电荷转移态的能量。
