Title : An electronic device that regulates the light phase of photosynthesis
Abstract:
Future Trends in Green Chemistry
Analytical studies of the three-dimensional structure of photosystems I and II have made it possible to identify the electronic molecular devices they contain, determine their purpose, and describe their functioning. In H2O-plastoquinone oxidoreductase (PS-ΙΙ), a quantum electron generator electron was discovered in the form of Mn4O5Ca(Н2О)4 manganese cluster, which has a chair configuration. Oxygen and manganese atoms are located in the corners of the cluster, in alternating order. Such spatial configuration promotes the formation of hydrogen bonds between the oxygen atoms of the cluster and the hydrogen atoms of water. At the same time, the oxygen atom of water is oriented towards the manganese atom of the cluster. Two subunits of the H2O-plastoquinone oxidoreductase enzyme contain 108 photoexcitable molecules with semiconductor properties. When exposed to light quanta, the conformation of the enzyme and the cluster changes being succeeded by the breakage of chemical bonds of water and the formation of two protons and atomic oxygen. The highly active atomic oxygen in water forms hydrogen peroxide, which is oxidized to Mn4+ forming molecular oxygen ↑O2. The reaction proceeds with the release of heat and the reduction of manganese to Mn2+. The regeneration of Mn4+ occurs with the transfer of 2 electrons along one of the branches of the active center P680 in PS-I.
It has been established that the active center of P680 has two branches of electron transport, although in practice it uses only one. When examining the structure of the active center, it is clear that P680 is a classical photoelectrolyzer. The photoelectrolyzer consists of two branches formed by pairs of molecules: chlorophyll, pheophytin and plastoquinone, which are closed by an “AND” trigger, which is non-heme iron Fe(Cys)4.
The cathode and anode of the photoelectrolyzer are represented by the paired chlorophyll molecules Chl1 and Chl2. The Fe(Cys)4 trigger, with the forward output on, directs electrons along one of the paths to reduce PQ to PQH2.
If the ETC for some reason is not capable of ensuring the electron transport. The “AND” trigger closes the photoelectrolyzer circuit, which is accompanied by the electrochemical decomposition of water and the formation of molecular ↑O2 and ↑H2. Thus, the excess electrons are removed from the biosystem.
The Rieske protein transfers electrons to the active site of P700 PS-Ι, which is a photoelectrolyzer. The operating principle of the photoelectrolyzer is similar to its functioning in PS-ΙΙ. The iron-sulfur cluster Fx (Fe4S4) controls the flow of electrons along the branches of the photoelectrolyzer.
Trigger FA, FB “OR” shows up in the protein structure, which, when switched on directly, directs electrons to reduce NADP+ to NADPH·H with the participation of the enzyme Ferredoxin NADP reductase. In the absence of the oxidized form of NADP+, the “OR” trigger switches the flow of electrons to reduce protons to molecular hydrogen in reaction with Hydrogenase.
