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Allosteric regulation of the light-harvesting system of photosystem II Horton P; Ruban AV; Wentworth MPhilos Trans R Soc Lond B Biol Sci 2000[Oct]; 355 (1402): 1361-70Non-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.|*Photosystem II Protein Complex[MESH]|Allosteric Regulation[MESH]|Chlorophyll[MESH]|Chloroplasts/metabolism[MESH]|Energy Metabolism[MESH]|Light[MESH]|Light-Harvesting Protein Complexes[MESH]|Models, Biological[MESH]|Photosynthesis/*physiology[MESH]|Photosynthetic Reaction Center Complex Proteins/*metabolism[MESH]|Plant Leaves/metabolism[MESH]|Plant Proteins/metabolism[MESH] |
