In 1961, Peter Mitchell propounded this view in the case of chloroplast and mitochondria. He’s been awarded 1978 Nobel Prize in Chemistry for this discovery.
The relation between the potential energy present within a concentration gradient of ions across a membrane and the use of this potential energy in the formation of ATP is explained by this hypothesis.
According to this view, a proton gradient is produced by electron transport, both in respiration and photosynthesis.
In the outer chamber or intermembrane space of mitochondria and inside the thylakoid lumen in chloroplasts, the gradient develops.
Thylakoid lumen is enriched with H+ ion on the outside of the thylakoid membrane due to photolytic splitting of the primary electron acceptor of water. The electrons are transferred to an H-carrier. When transporting an electron to the carrier, the carrier removes a proton from the stroma membrane ‘s inner side.
While the electron moves to the next carrier, the proton is released into the lumen.
NaDP reductase is located on the outside of the membrane of the thylakoid.
It obtains electrons from PS I and protons from the matrix to reduce the state of NaDP+ to NaDPH+ H+.
The effect of the three events is that proton concentration decreases in the region of the matrix or stroma, while thylakoid lumen concentration increases, resulting in a decrease in pH.
Across the thylakoid, a proton gradient develops.
Due to proton movement through transmembrane channels, CF0 of ATPase (CF0-CF1 particle), the proton gradient is broken down.
The rest of the membrane is H+ impermeable. CF0provides H+ or protons with facilitated diffusion.
When protons move to the other side of ATP synthase, they cause conformative changes in the ATPase or coupling factor CF1 particle.
ATP from ADP and inorganic phosphate form the transient CF1 particle of the ATPase enzyme.
Therefore, chemiosmosis-based ATP synthesis requires a membrane, a proton pump, a proton gradient and CF0 – CF1 particle or ATPase.
One molecule of ATP is formed when 3H+ pass through ATP synthase.
