2023-07-12 04:00:01
When photosynthetic cells absorb sunlight, packets of energy leap between a series of light-catching proteins until they reach the photosynthetic reaction center. This is where cells convert energy (In common sense, energy is anything that does work, makes energy, etc.) into electrons, which then fuel the production of sugar molecules.
Plant cells with visible chloroplasts.
Credit: Wikipedia
This transfer of energy within the light-collecting complex occurs with very high efficiency: almost every photon of absorbed light generates an electron (The electron is an elementary particle of the lepton family, and has a charge…), a phenomenon known as quasi-unit quantum efficiency.
A new study by MIT chemists offers a potential explanation for the high efficiency of these light-harvesting proteins, also called antennae. For the first time, the researchers were able to measure the energy transfer between these proteins, revealing that their disordered arrangement improves the efficiency of energy transduction.
“For this antenna to work, it requires long-range energy transduction. Our finding is that the disordered organization of light-harvesting proteins enhances the efficiency of this long-range energy transduction” , says Gabriela Schlau-Cohen, associate professor of chemistry at MIT and lead author of the new study.
In this study, the MIT team focused its attention on purple bacteria, often found in oxygen-poor aquatic environments and frequently used as model for studies of capture (A capture, in the field of astronautics, is a process by which a celestial object, which…) of light by photosynthesis (Photosynthesis (Greek φῶς phōs, light and…) .
Within these cells, captured photons travel through light-harvesting complexes made up of light-absorbing proteins and pigments, such as chlorophyll. Using ultrafast spectroscopy, a technique that uses extremely short laser pulses to study events occurring on femtosecond to nanosecond time scales, scientists have been able to study how energy moves inside of one of these proteins. However, the study of the displacement ( In geometry, a displacement is a similarity that conserves distances and angles…) of the energy between these proteins has proven to be much more difficult, because it requires positioning several proteins of controlled way.
For this study, the researchers integrated two versions of the main light-capturing protein found in purple bacteria, known as LH2 and LH3, into their nanodisks. LH2 is the protein present in normal light conditions, and LH3 is a variant usually expressed only in low light conditions.
Because LH2 and LH3 absorb different wavelengths of light, it is possible to use ultrafast spectroscopy to observe the energy transfer between them. For close proteins, the researchers found that it takes regarding 6 picoseconds for a photon to travel between them. For more distant proteins, the transfer takes up to 15 picoseconds.
The faster travel results in a more efficient transfer of energy, because the longer the travel, the more energy is lost during the transfer.
The researchers also found that proteins arranged in a lattice structure showed less efficient energy transfer than proteins arranged in randomly organized structures, as they typically are in living cells.
“Now that we have established the ability to measure energy transfer between proteins, we plan to explore energy transfer between other proteins,” says Gabriela Schlau-Cohen.
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