Allosteric regulation of the light-harvesting system of photosystem II.
Non-photochemical quenching of chlorophyll fluorescence (NPQ) is symptomatic of the regulation of energy dissipation by the light-harvesting antenna of photosystem II (PS II). The kinetics of NPQ in both leaves and isolated chloroplasts are determined by the transthylakoid delta pH and the de-epoxidation state of the xanthophyll cycle. In order to understand the mechanism and regulation of NPQ we have adopted the approaches commonly used in the study of enzyme-catalysed reactions. Steady-state measurements suggest allosteric regulation of NPQ, involving control by the xanthophyll cycle carotenoids of a protonation-dependent conformational change that transforms the PS II antenna from an unquenched to a quenched state. The features of this model were confirmed using isolated light-harvesting proteins. Analysis of the rate of induction of quenching both in vitro and in vivo indicated a bimolecular second-order reaction; it is suggested that quenching arises from the reaction between two fluorescent domains, possibly within a single protein subunit. A universal model for this transition is presented based on simple thermodynamic principles governing reaction kinetics.
Horton
P
P
Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, UK. p.horton@sheffield.ac.uk
Ruban
A V
AV
Wentworth
M
M
D000494:Allosteric Regulation; D002734:Chlorophyll; D002736:Chloroplasts / Q000378:metabolism; D004734:Energy Metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008954:Models, Biological; D010788:Photosynthesis / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll