A Scrutiny of Mitchell's Chemiosmotic Hypothesis of Respiratory Chain and Photosynthetic Phosphorylation

Publisher Summary This chapter explains Mitcheirs chemiosmotic hypothesis of respiratory chain and photosynthetic phosphorylation. Energy is extracted from hydrogen or electron transport in three regions of the respiratory chain between NADH and O 2 , and this energy is used to drive ATP synthesis, uptake of metal cations by the mitochondrion, and pyridine nucleotide transhydrogenation. Studies with the inhibitor atractyloside show that adenine nucleotides have to approach the ATP in the mitochondrial membrane from the inner side; ATP enters the inner compartment in exchange for ADP, or vice versa, by means of an adenine nucleotide translocase in the membrane. As there is an electrical component of the protonmotive force and also an osmotic component, the chemiosmotic hypothesis is better known as the electrochemical hypothesis, although protontranslocation hypothesis might have advantages. The pH rise represents the difference between two opposing processes, a light-driven uptake and a leakage back of protons, and in the steady state, the rates of uptake and leakage are equal. Witt and colleagues maintain that chlorophyll b is responsible for the extinction changes at 515 mμ, which are presumably because of the action of the electric field on the optical properties of this pigment, that is, inter alia to the Stark effect