Zaks 2012, Proc. Natl. Acad. Sci.

The Zaks 2012 model is a detailed kinetic model of the rapidly reversible, pH-dependent component of non-photochemical quenching (qE) in photosystem II (PSII). It was developed to quantify how the lumen pH controls the dissipation of excess excitation energy as heat, and it does so by resolving the molecular events that sense and respond to lumen acidification: the protonation of the PsbS protein, the deepoxidation of violaxanthin to antheraxanthin and zeaxanthin by violaxanthin deepoxidase (the xanthophyll cycle), and the resulting switch of PSII antennae into a quenched state. Around this regulatory core it represents the photochemistry and electron transport of PSII in fine detail — excited and oxidised P680 states, the pheophytin and Q_A/Q_B acceptors, the plastoquinone pool, cytochrome b6f, plastocyanin and PSI — together with ATP synthase, proton leak and the lumen ion fluxes (Mg²⁺, Cl⁻, K⁺) that buffer the proton-motive force.

By coupling these processes, the model predicts qE directly from PsbS protonation and zeaxanthin accumulation and reproduces the dynamics of chlorophyll fluorescence quenching and its relaxation. It is one of the most mechanistically explicit treatments of NPQ available and complements the more reduced quenching descriptions used elsewhere; it is included in GreenSloth as a reference for how the photoprotective machinery of PSII can be modelled at the level of individual redox and protonation states.

Scheme

© - Proc. Natl. Acad. Sci.

Model definition