Rajagopal Subramanyam, Egorova Elena A, Bukhov Nikolai G, Carpentier Robert
Groupe de Recherche en Energie et Information Biomoléculaires, Université du Québec à Trois-Rivières, 3351 Boulevard des Forges, Three Rivers, Quebec, Canada GA9 5H7.
Biochim Biophys Acta. 2003 Sep 30;1606(1-3):147-52. doi: 10.1016/s0005-2728(03)00111-7.
The ability of three substituted quinones, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), 2,6-dichloro-p-benzoquinone (DCBQ), and tetramethyl-p-benzoquinone (duriquinone) to quench the excited states of chlorophyll (Chl) molecules in Photosystem I (PSI) was studied. Chl fluorescence emission measured with isolated PSI submembrane fractions was reduced following the addition of exogenous quinones. This quenching progressively increased with rising concentrations of the exogenous quinones according to the Stern-Volmer law. The values of Stern-Volmer quenching coefficients were found to be 3.28 x 10(5) M(-1) (DBMIB), 1.31 x 10(4) M(-1) (DCBQ), and 3.7 x 10(3) M(-1) (duroquinone). The relative quenching capacities of the various exogenous quinones in PSI thus strictly coincided to those found for the quenching of Fo level of Chl fluorescence in isolated thylakoids, which is emitted largely by Photosystem II (PSII) [Biochim. Biophys. Acta (2003) 1604, 115-123]. Quenching of Chl excited states in PSI submembrane fractions by exogenous quinones slowed down the rate of P700, primary electron donor of PSI, photooxidation measured at limiting actinic light irradiances thus revealing a reduced photochemical capacity of absorbed quanta. The possible involvement of non-photochemical quenching of excited Chl states by oxidized phylloquinones, electron acceptors of PSI, and oxidized plastoquinones, mobile electron carriers between PSII and the cytochrome b(6)/f complex, into the control of photochemical activity of PSI is discussed.
研究了三种取代醌，即2,5-二溴-3-甲基-6-异丙基对苯醌（DBMIB）、2,6-二氯对苯醌（DCBQ）和四甲基对苯醌（杜醌）猝灭光系统I（PSI）中叶绿素（Chl）分子激发态的能力。加入外源醌后，用分离的PSI亚膜组分测得的Chl荧光发射降低。根据斯特恩-沃尔默定律，这种猝灭随着外源醌浓度的升高而逐渐增加。发现斯特恩-沃尔默猝灭系数的值分别为3.28×10⁵ M⁻¹（DBMIB）、1.31×10⁴ M⁻¹（DCBQ）和3.7×10³ M⁻¹（杜醌）。因此，PSI中各种外源醌的相对猝灭能力与在分离的类囊体中Chl荧光Fo水平猝灭时发现的能力严格一致，Chl荧光Fo水平主要由光系统II（PSII）发射[生物化学与生物物理学报（2003年）1604, 115 - 123]。外源醌对PSI亚膜组分中Chl激发态的猝灭减慢了PSI的初级电子供体P700在极限光化光辐照度下的光氧化速率，从而揭示了吸收量子的光化学能力降低。讨论了氧化的叶绿醌（PSI的电子受体）和氧化的质体醌（PSII与细胞色素b₆/f复合物之间的移动电子载体）对激发态Chl的非光化学猝灭可能参与PSI光化学活性控制的情况。
