title: Equilibrium between quenched and nonquenched conformations of the major plant light-harvesting complex studied with high-pressure time-resolved fluorescence.
abstract: Nonphotochemical quenching (NPQ) of chlorophyll fluorescence plays an important role in the protection of plants against excessive light. Fluorescence quenching of the major light-harvesting complex (LHCII) provides a model system to study the mechanism of NPQ. The existence of both quenched and nonquenched states of LHCII has been postulated. We used time-resolved fluorescence and hydrostatic pressure to study differences between these states. Pressure shifts the thermodynamic equilibrium between the two states. The estimated volume difference was 5 mL/mol, indicating a local conformational switch. The estimated free energy difference was 7.0 kJ/mol: high enough to keep the quenched state population low under normal conditions, but low enough to switch in a controlled way. These properties are physiologically relevant properties, because they guarantee efficient light harvesting, while at the same time maintaining the capacity to switch to a quenched state. These results indicate that conformational changes of LHCII can play an important role in NPQ.
authors.affiliation: Laboratory of Biophysics, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands. bart.vanoort@wur.nl
authors.forename: Bart
authors.initials: B
authors.lastname: van Oort
authors.forename: Arie
authors.initials: A
authors.lastname: van Hoek
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ruban
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011312:Pressure; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D003313:Zea mays
chemical_list: D045332:Photosystem II Protein Complex