Redox Regulation shown by proteins involved in Photosynthesis

What is Redox Regulation?

Redox Regulation is the activation and deactivation of the proteins that are involved in photosynthesis. The activation and deactivation of proteins occurs when there are changes in the their redox (reduction and oxidation) states.

What is Photosynthesis?

Photosynthesis as we know is the process in which the plants make their food in the presence of sunlight. During photosynthesis, the proteins that are involved in the process need to be activated and perform their function when there is sunlight. In the absence of sunlight, photosynthesis does not occur and the proteins need to be in an idle or non-functioning state.

The switching ‘on’ and ‘off’ of proteins is done by the process of Redox Regulation. In other words, the activation and deactivation of proteins occurs due to the changes in their redox (reduction and oxidation) states.

How does Redox Regulation take place?

When there is light, the ferredoxin-thioredoxin reductase (FTR)/thioredoxin (Trx) pathway comes into play for the reduction process to occur. This in turn activates the photosynthesis process to take place.

The scientists were not sure about the role of the proteins in the absence of light and how the plant proteins function again in the presence of light for the photosynthetic activity.

The scientists at Tokyo Tech have discovered two proteins which respond to the changes in light conditions that make photosynthesis very effective.

Keisuke Yoshida, Toru Hisabori and their colleagues have discovered that two proteins help in the reoxidation of the proteins involved in the photosynthetic activity. The two proteins make up the thioredoxin-like2 (TrxL2)/2-Cysperoxiredoxin (2CP) redox regulation process by modifying the key molecular players. These two proteins take the energy from the photosynthetic proteins to the energy hungry hydrogen peroxide.

TrxL2 is responsible for the switching off process and though it oxidizes many proteins, it only reduces2CP, which allows the energy that has been drained by TrxL2 from some reactions to pass to 2CP and then to the hydrogen peroxide. This goes on and keeps the photosynthetic activity on standby until light is available again.

TrxL2/2CP also performs their work in the presence of light, but the normal process in plants overshadows their activity. They function predominantly in the absence of light. In mutant plants where 2CP is absent photosynthesis takes place normally but the switching off mechanism does not perform as efficiently than was is observed in wildplants.

Since it appears that the process is less efficient and not completely absent indicates that there are still other yet to be discovered proteins which may perform similar functions in plants. The scientists are thus able to show how the activity of the proteins involved in photosynthesis is reserved for the time when it is actually needed.

From this we can see how the Redox Regulation in plants control photosynthesis. Though the redox regulation in plants was well known during photosynthesis, i.e.in the presence of light, this mechanism of redox regulation was not really understood in the absence of light.

The study carried out shows that energy is syphoned from the proteins to TrxL2 to 2CP and then to hydrogen peroxide. During this time, photosynthesis is on standby until there is light available again.