Schulten Els A M, Matysik Jörg, Kiihne Suzanne, Raap Jan, Lugtenburg Johan, Gast Peter, Hoff Arnold J, de Groot Huub J M
Leiden Institute of Chemistry, Gorlaeus Laboratoria, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
Biochemistry. 2002 Jul 9;41(27):8708-17. doi: 10.1021/bi025608u.
Reaction centers of wild-type Rhodobacter sphaeroides were selectively (13)C-isotope labeled in bacteriochlorophyll and bacteriopheophytin. (13)C solid-state CP/MAS NMR and photo-CIDNP were used to provide insight into the electronic structure of the primary electron donor and acceptor on the atomic scale. The first 2-dimensional photochemically induced dynamic nuclear polarization (photo-CIDNP) (13)C-(13)C solid-state MAS NMR spectra reveal that negative charging of the two BChl rings of the primary donor is involved in ground-state tuning of the oxidation potential of these cofactors in the protein via local electrostatic interactions. In particular, the (13)C shifts show moderate differences in the electronic structure between the two BChl molecules of the special pair in the electronic ground state, which can be attributed to hydrogen bonding of one of the BChl molecules. The major fraction of the electron spin density is strongly delocalized over the two BChl molecules of the special pair and the photochemically active BPhe. A small fraction of the pi-spin density is distributed over a fourth component, which is assigned to the accessory BChl. Comparison of the photo-CIDNP data with "dark" NMR spectra obtained in ultra high field indicates a rigid special pair environment upon photoreaction and suggests that structural changes of the aromatic macrocycles of the two BChl molecules of the special pair do not significantly contribute to the reorganization energy associated with the charge-transfer process.
野生型球形红细菌的反应中心在细菌叶绿素和细菌脱镁叶绿素中被选择性地进行了（13）C同位素标记。使用（13）C固态交叉极化/魔角旋转核磁共振（CP/MAS NMR）和光化学诱导动态核极化（photo-CIDNP）来在原子尺度上深入了解初级电子供体和受体的电子结构。最初的二维光化学诱导动态核极化（photo-CIDNP）（13）C-（13）C固态魔角旋转核磁共振光谱表明，初级供体的两个细菌叶绿素环的负电荷通过局部静电相互作用参与蛋白质中这些辅因子氧化电位的基态调节。特别是，（13）C位移显示出处于电子基态的特殊对的两个细菌叶绿素分子之间在电子结构上存在适度差异，这可归因于其中一个细菌叶绿素分子的氢键作用。电子自旋密度的主要部分在特殊对的两个细菌叶绿素分子和光化学活性细菌脱镁叶绿素上强烈离域。一小部分π自旋密度分布在第四个组分上，该组分被指定为辅助细菌叶绿素。将光化学诱导动态核极化（photo-CIDNP）数据与在超高场获得的“暗”核磁共振光谱进行比较，表明光反应时特殊对环境刚性，并且表明特殊对的两个细菌叶绿素分子的芳香大环的结构变化对与电荷转移过程相关的重组能没有显著贡献。
