Meler reaction

The Meler reaction is the reduction of oxygen O ₂ to the superoxide anion radical O ₂ ^{- ·} using electrons obtained from ferredoxin or 4Fe-4S clusters of photosystem I ^[1] . The reaction occurs under conditions of excessive illumination, when the pool of ferredoxins and NADP ^{+ is} re-reduced and photosystem I has nowhere to dump electrons. The superoxide anion is then converted to hydrogen peroxide (H ₂ O ₂ ) and O ₂ under the influence of the superoxide dismutase enzyme, and H ₂ O _{2 is} converted into water by the ascorbate peroxidase enzyme. Electrons for oxygen reduction are formed from water and eventually return to water, forming a cycle. Therefore, the process is called pseudocyclic electron transport. It is similar to cyclic transport in that NADPH is not synthesized, but only ATP . However, under the Mehler reaction conditions, the ATP / ADP ratio is often high, so the available amount of ADP is not enough for ATP synthesis. As a result, during the Mehler reaction, a very high proton gradient is created on the thylakoid membrane ^[2] .