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Photosystem I

Photosystem I

Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...

Photosystem II

Photosystem II

The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...

Photosystems

Photosystems

Photosystems are multiprotein complexes that form the functional units of photosynthesis in plants, algae, and cyanobacteria. They are found embedded in the membrane of tiny sac-like structures called thylakoids placed inside the chloroplast.
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...

The Z-Scheme of Electron Transport in Photosynthesis

The Z-Scheme of Electron Transport in Photosynthesis

The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...

The Photochemical Reaction Center

The Photochemical Reaction Center

Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...

Oxygenic Photosynthesis

Oxygenic Photosynthesis

Oxygenic photosynthesis is a fundamental process in which light energy is harnessed to drive the oxidation of water, leading to the production of molecular oxygen (O₂), adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). This process is essential for sustaining aerobic life on Earth and is primarily carried out by cyanobacteria, algae, and plants. The core of oxygenic photosynthesis lies in the thylakoid membranes, where chlorophyll pigments facilitate light...

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Related Experiment Video

Updated: Jun 13, 2026

Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting

Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting

Published on: February 14, 2019

Two different charge separation pathways in photosystem II.

Elisabet Romero¹, Ivo H M van Stokkum, Vladimir I Novoderezhkin

¹Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. eli@few.vu.nl

|April 27, 2010

Summary

This summary is machine-generated.

Investigating charge separation in Photosystem II reaction centers reveals two distinct ultrafast pathways driven by protein motion and excited states. At low temperatures, these pathways can be either fast and activation-less or slow and activated.

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Last Updated: Jun 13, 2026

Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting

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Published on: October 5, 2019

Area of Science:

Photosynthesis research
Biophysics of energy conversion
Plant biochemistry

Background:

Charge separation is crucial for converting solar energy into chemical energy.
Photosystem II (PSII) reaction centers are key sites for this initial energy conversion.
Understanding the dynamics of charge separation is vital for artificial photosynthesis.

Purpose of the Study:

To investigate the mechanisms of ultrafast charge separation in spinach Photosystem II reaction centers.
To identify the excited states and pathways involved in charge separation at low temperatures.
To elucidate the role of protein dynamics in charge separation efficiency.

Main Methods:

Transient absorption experiments were conducted at 77 K.
Isolated Photosystem II reaction center preparations from spinach were used.
Global and target analysis were employed to interpret the experimental data.

Main Results:

At least two distinct excited states, (Chl(D1)Phe(D1))* and (P(D1)P(D2)Chl(D1))*, were identified.
These excited states lead to two different pathways for ultrafast charge separation.
Slow protein motions contribute to energetic differentiation and distinct charge separation pathways.
Two excitation energy trap states were observed at low temperatures, leading to long-timescale charge-separated states.

Conclusions:

The study concludes that protein disorder influences charge separation pathways.
At 77 K, charge separation can occur via both activation-less, fast pathways and activated, slow pathways.
The identified excited states are implicated in both ultrafast and slow charge separation processes at low temperatures.