The plastoquinone pool as possible hydrogen pump in photosynthesis

Area of Science:

• Photosynthesis research
• Chloroplast function
• Bioenergetics

Background:

• The thylakoid membrane facilitates proton gradients essential for ATP synthesis.
• The precise mechanism of proton transport by the plastoquinone pool remains under investigation.

Purpose of the Study:

• To investigate the role of the plastoquinone pool in vectorial hydrogen (H+ + e-) transport across the thylakoid membrane.
• To determine the stoichiometry and kinetics of proton and electron movement linked to plastoquinone redox reactions.

Main Methods:

• Utilized isolated spinach chloroplasts.
• Measured optical changes reflecting plastoquinone redox state.
• Monitored external H+ uptake and internal H+ release.

Main Results:

• Established a 1:1:1 stoichiometric coupling between external H+ uptake, electron translocation via plastoquinone, and internal H+ release.
• Demonstrated identical rates for electron release from plastoquinone and proton release into the thylakoid space under far-red illumination.

Conclusions:

• The plastoquinone pool functions as a pump for vectorial hydrogen (H+ + e-) transport across the thylakoid membrane.
• Protons are translocated with electrons through the plastoquinone pool from the exterior to the interior.
• The study discusses the molecular mechanism and contrasts this hydrogen pump with proton pumps in Halobacteria.