In the plant body, multiple enzymes involved in photosynthesis are reduced (switched on) as the light becomes stronger in the morning.On the other hand, when the light becomes weak at dusk, these enzymes are oxidized (switched off).The mechanism that regulates the enzyme activity in this way is called "redox control", and the formation / cleavage (oxidation / reduction) of the disulfide bond possessed by the enzyme protein is controlled according to the redox state in the living body.

　When the switch is turned on, a redox protein called thioredoxin reduces and cleaves the disulfide bond of the target enzyme, thereby changing the enzyme from the inactive form to the active form.This on-side mechanism has been known for a long time, but the molecular mechanism for turning it off has not been clarified.

　The research team focused on the unknown-function protein "thioredoxin-like2" (TrxL2), which has an amino acid sequence similar to thioredoxin. Examination of the properties of TrxL2 revealed that it is an oxidative factor protein that has a significantly higher redox potential than thioredoxin and transfers reducing power in the opposite direction to thioredoxin.Furthermore, it was found that the reducing power is passed to 2-Cys Prx, which uses the reducing power to eliminate active oxygen harmful to cells in order to continue to oxidize the enzyme of photosynthesis.In other words, by utilizing the strong oxidizing power of active oxygen, it is said that continuous protein oxidation is performed.

　This result elucidated a part of the mechanism to prevent energy waste by putting the enzymes involved in photosynthetic glucose metabolism to sleep at night when plants cannot perform photosynthesis.In the future, it is expected to be an important guideline for application development such as design of environment-adaptive crops.

Paper information:[Proceedings of the National Academy of Sciences] Thioredoxin-like2 / 2-Cys peroxiredoxin redox cascade supports oxidative thiol modulation in chloroplasts