tilakoidilumen

The thylakoid lumen is the internal compartment enclosed by the thylakoid membrane within chloroplasts and cyanobacteria. It is a crucial space for the light-dependent reactions of photosynthesis. Protons are pumped from the stroma into the thylakoid lumen by the electron transport chain, which is embedded in the thylakoid membrane. This proton pumping creates a proton gradient across the membrane, with a higher concentration of protons in the lumen compared to the stroma.

This electrochemical gradient is then used by ATP synthase to produce ATP, the energy currency of the cell. The lumen also plays a role in the splitting of water molecules, a process that releases oxygen, electrons, and protons into the lumen. The accumulation of protons within the lumen is a key step in harnessing light energy to drive ATP synthesis. The lumen's acidic environment, maintained by proton accumulation, is essential for the function of certain enzymes involved in photosynthesis. The lumen acts as a reservoir for protons that are released back into the stroma through ATP synthase.