This view was propounded by Peter Mitche!! in 1961 in
the case of mitochondria and chloroplast. He was awarded
the Nobel Prize for Chemistry in 1978 for this discovery
. This hypothesis explains the relationship 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 According to this view, electron transport, both in respiration
and photosynthesis produces a proton gradient.
The gradient develops in the outer chamber or intermembrane space of mitochondria and inside the thylakoid lumen in chloroplasts
Lumen of thylakoid becomes enriched with H" ion due to
photolytic splitting of water.
Primary acceptor of electron is located on the outerside of thylakoid membrane.
It transfers its electrons to an H-carrier. The carrier removes a proton from stroma while transporting electron to the
innerside of membrane.
The proton is released into the lumen while the electron
passes to the next carrier.
. NADP reductase is situated on the outerside of thylakoid It obtains electron from PS I and protons from matrix to
. The consequences of the three events is that concentration
membrane.
reduce NADP+ to NADPH+H+ state.
of protons decreases in matrix or stroma region while their
concentration in thylakoid lumen rises resulting in decrease in ph A proton gradient develops across the thylakoid.
The proton gradient is broken down due to movement of
protons through transmembrane channels, CFo of ATPase
(CFo - CFi particle).
The rest of the membrane is impermeable to Ht. CFo
provides faciliated diffusion to H+ or protons.
. As protons move to the other side of ATP synthase, they bring about conformational changes in CFi particle of
ATPase or coupling factor.
The transient CF1 particle of ATPase enzyme form ATP from ADP and inorganic phosphate.
Therefore, ATP synthesis through chemiosmosis requires a membrane, a proton pump, a proton gradient and
CFo CFi particle or ATPase.
One molecule of ATP is formed when 3H+ pass through ATP synthase.
