Rhodopseudomena viridis细菌光合作用反应中心质体醌Q_A 与泛醌Q_B 间电子转移耦合质子转移机理的理论研究(英文)

Theoretical Studies on the Mechanism of the Proton-transfer-coupled Electron Transfer Reactions Between Menaquinone Q_A and Ubiquinone Q_B in the Bacterial Photosynthetic Reaction Center of Rhodopseudomona viridis

用量子化学B3LYP/ 6 - 31G(d)方法 ,对Rhodopseudomenaviridis细菌光合反应中心质体醌QA(MQ1)与泛醌QB(UQ1)间的电子转移耦合质子转移 (PT_ET)机理进行了研究。对反应 (1)之后的Gibbs自由能变化进行了计算。结果表明 ,(1)按照各反应的数值 ,在无耦合质子转移的情况下 ,UQ1不可能由MQ-1连续接受两个电子。由于ΔG02b 0 ,ΔG03b 0和ΔG04b 0 ,相应的PT ET反应将依序沿 (2b)、(3b)及 (4b)进行。 (2 )在气相情况下 ,由于周围的氨基酸残基或水分子转移到UQ1的第一个及第二个质子 (H+ (1)和H+ (2 ) )将先后分别与UQ1的No.7和No .8氧原子结合 ;在蛋白环境情况下 (SCRF方法 ,ε =4 .0 ) ,质子耦合的顺序正相反 ,但H+ (1)和H+ (2 )与UQ-1结合的能量传递差很小。在气相及SCRF模拟环境中 ,相同反应间的ΔG0 无显著差别。 (3)MQ-1间UQ-1的PT ET反应如下 : MQ1-+UQ1→MQ1+UQ1-(1) UQ1-(O( 7) ) +H+ (HisL190 )→UQ1H (2b) (Gas)or UQ1-(O( 8) ) +H+ (H2 O)→UQ1H (2b’) (SCRF)or UQ1-(O( 8) ) +H+ (ArgL2 17)→UQ1H (2b’) (SCRF) MQ1-+UQ1H→MQ1+UQ1H-(3b) (Gas) MQ1-+UQ1H→MQ1+UQ1H-(3b’) (SCRF) UQ1H-+H+ (H2 O)→UQ1H2 (4b) (Gas)or UQ1H-+H+ (ArgL2 17)→UQ1H2 (4b) (Gas)or UQ1H-+H+

The mechanism of the proton_transfer_coupled electron transfer (PT_ET) reactions between the menaquinone Q A (MQ 1) and ubiquinone Q B (UQ 1) in the bacterial photosynthetic reaction center of Rhodopseudomona viridis was studied by using the B3LYP/6_31G(d) method. The changes of standard Gibbs free energy ΔG 0 of all possible reactions followed the ET reaction (1) were calculated. The results indicated that: (1) according to the ΔG 0 values of corresponding reactions, UQ 1 could not accept two electrons from MQ - 1 continually without the coupled proton transfer reactions. Because of ΔG 0 2b 0, ΔG 0 3b 0 and ΔG 0 4b 0, the corresponding PT_ET reactions could take place along with reactions (2b), (3b) and (4b) sequentially; (2) on the gaseous condition, the first and second transferred protons (H +(1) and H +(2)) from the surrounding amino acid residues or water molecules will combine with the oxygen No.7 and oxygen No.8 of UQ 1, respectively. On the condition of protein surroundings (by SCRF model, ε =4.0), the results are converse but the energy difference between the combination of H +(1) and H +(2) with UQ - 1 is quite small. The difference of ΔG 0 values between the corresponding reactions in gaseous surroundings and the SCRF model is not significant; (3) the PT_ET reactions between MQ 1 - and UQ 1 - should be as follows: MQ 1 -+UQ 1→MQ 1+UQ 1 - (1) UQ 1 - ( O (7) )+H +( HisL 190)→UQ 1H(2b) ( Gas ) or UQ 1 - ( O (8) )+H +(H 2O)→UQ 1H (2b') ( SCRF ) or UQ 1 - ( O (8) )+H + ( ArgL 217)→UQ 1H(2b') ( SCRF ) MQ 1 -+UQ 1H→MQ 1+UQ 1H - (3b) ( Gas ) MQ 1 -+UQ 1H→MQ 1+UQ 1H -(3b') ( SCR F) UQ 1H -+H +(H 2O)→UQ 1H 2(4b) ( Gas ) or UQ 1H -+H + ( ArgL 217)→UQ 1H 2 (4b) ( Gas ) or UQ 1H -+H + ( HisL 190)→UQ 1H 2 (4b') ( SCRF )