Equilibrium between Quenched and Nonquenched Conformations of the Major Plant Light-Harvesting Complex Studied with High-Pressure Time-Resolved Fluorescence

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• 作者：Bart van Oort ; Arie van Hoek ; Alexander V. Ruban ; Herbert van Amerongen
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：July 5, 2007
• 年：2007
• 卷：111
• 期：26
• 页码：7631 - 7637
• 全文大小：106K
• 年卷期：v.111,no.26(July 5, 2007)
• ISSN：1520-5207

文摘

Nonphotochemical quenching (NPQ) of chlorophyll fluorescence plays an important role in the protection ofplants against excessive light. Fluorescence quenching of the major light-harvesting complex (LHCII) providesa model system to study the mechanism of NPQ. The existence of both quenched and nonquenched states ofLHCII has been postulated. We used time-resolved fluorescence and hydrostatic pressure to study differencesbetween these states. Pressure shifts the thermodynamic equilibrium between the two states. The estimatedvolume difference was 5 mL/mol, indicating a local conformational switch. The estimated free energy differencewas 7.0 kJ/mol: high enough to keep the quenched state population low under normal conditions, but lowenough to switch in a controlled way. These properties are physiologically relevant properties, because theyguarantee efficient light harvesting, while at the same time maintaining the capacity to switch to a quenchedstate. These results indicate that conformational changes of LHCII can play an important role in NPQ.