Voltage changes involving photosystem II quinone-iron complex turnover

Area of Science:

• Photosynthesis research
• Bioenergetics
• Plant molecular biology

Background:

• Photosystem II (PSII) is crucial for oxygenic photosynthesis.
• Investigating electron and proton transfer mechanisms is key to understanding PSII efficiency.
• The role of the non-heme iron in PSII remains an area of active research.

Purpose of the Study:

• To investigate proton-coupled electron transfer between plastoquinone acceptor Q(A) and non-heme iron in PSII.
• To determine the location of the iron-quinone complex within the membrane.
• To elucidate the kinetics and mechanism of a submillisecond electrogenic phase.

Main Methods:

• Electrometrical technique using phospholipid vesicles.
• Incorporation of PSII core particles into proteoliposomes.
• Kinetic analysis of transmembrane electric potential difference (Deltapsi) generation after laser flashes.
• Effect of D(2)O and temperature on reaction rates.

Main Results:

• The iron-quinone complex faces the interior of the proteoliposome membrane.
• A submillisecond electrogenic phase (approx. 0.1 ms) was observed after the first laser flash.
• This phase was absent on subsequent flashes or in the presence of DCMU.
• The rate of this phase is reduced by D(2)O and lower temperatures.

Conclusions:

• The submillisecond electrogenic phase is attributed to vectorial proton transfer to amino acid residues near the non-heme iron.
• This finding suggests a potential role for non-heme iron in cyclic electron transfer within PSII.
• The study provides new insights into the intricate mechanisms of charge separation and proton movement in PSII.