A high-potential redox component located within cyanobacterial photosystem II

Area of Science:

• Photosynthesis research
• Cyanobacterial bioenergetics
• Plant physiology

Background:

• Oxygen evolution is crucial for photosynthesis.
• Photosystem II (PSII) drives water oxidation.
• Calcium ions (Ca2+) are known cofactors in oxygen evolution.

Purpose of the Study:

• To investigate the redox properties of oxygen evolution in Phormidium luridum.
• To elucidate the role of calcium and redox potential in PSII activity.
• To propose models for high-potential redox components in PSII.

Main Methods:

• Studied oxygen evolution using ferricyanide and benzoquinone as Hill oxidants.
• Measured oxygen evolution rates across a range of solution redox potentials (+350 to +550 mV).
• Examined both 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-sensitive and -insensitive activities.

Main Results:

• Phormidium luridum showed selective oxygen evolution with ferricyanide over benzoquinone.
• Oxygen evolution rate increased with higher redox potential.
• Calcium (Ca2+) addition remained essential regardless of redox potential or oxidant used.
• DCMU-sensitive and -insensitive activities exhibited similar redox-dependent properties.

Conclusions:

• A high-potential redox component (> +450 mV) likely exists within PSII.
• Two models are proposed: a competing donor or a high-potential primary acceptor.
• These findings offer insights into the intricate electron transfer mechanisms in cyanobacterial photosynthesis.