thylakoïdlumen

The thylakoid lumen is the internal compartment enclosed by the thylakoid membrane within chloroplasts and cyanobacteria. This membrane is crucial for photosynthesis, where light energy is converted into chemical energy. The lumen plays a vital role in the light-dependent reactions of photosynthesis.

During the light-dependent reactions, water molecules are split, a process called photolysis, which releases protons (H+) into the thylakoid lumen. Simultaneously, protons are pumped from the stroma, the fluid-filled space outside the thylakoid membrane, into the lumen by the electron transport chain. This accumulation of protons creates a proton gradient, with a higher concentration of H+ inside the lumen compared to the stroma.

This proton gradient represents a form of potential energy. As protons flow back into the stroma through an enzyme called ATP synthase, this energy is harnessed to produce adenosine triphosphate (ATP), a key energy currency of the cell. The thylakoid lumen's unique environment and its role in proton accumulation are therefore essential for efficient ATP production during photosynthesis. The lumen is also where oxygen is released as a byproduct of water splitting.