BCH/PPA 503 -- Plant
Biochemistry
Lecture Eight

ATP Synthesis, Chemiosmotic Hypothesis, and H+ Transport

Outline

CF0/CF1 ATP Synthase

 

 

Remember the energy of a photon depends on its wavelength, according to the equation

Expressed in molar terms, an Einstein is the amount of energy in Avogadro's number of photons: 

 

Light of 700 nm is the longest wavelength and lowest energy light acting in plant photosystems.  An Einstein of 700 nm light is equivalent in energy to ~170 kJ.  Eight Einsteins of this light, 1360 kJ, theoretically generate 2 moles of NADPH, 2 -3 moles of ATP and 1 mole of O2.

Light driven ATP synthesis, photophosphorylation, is chemiosmotic.  During photosynthesis protons accumulate on the lumen side of thylakoid membranes setting up a proton gradient.  This establishes an electrochemical gradient, or proton-motive force, across the thylakoid membranes providing the energy for ATP synthesis as protons are vectorially transported to the stroma through the ATP synthase complexes.  At least 3 H+ must be translocated for every ATP synthesized. The 1st direct evidence for the chemiosmotic hypothesis was obtained by Jagendorf and Uribe in elegantly simple experiments with isolated chloroplasts.

This is animated in the third figure on Anthonie Muller's page.

 

This proton motive force actually causes the ATP synthase complex to spin with the spinning transducing the energy required for ATP synthase like a water wheel. This was demonstrated in the experiment of Masasuke Yoshida as described in lecture. As mentioned the F1-ATPase was tethered to a glass surface by the b-subunit. The motion was detected by attaching a fluorescent group to make it visible, and recorded using a video camera attached to a microscope (see illustration from Junge et al. TIBS article, below). The actual video can be viewed here.

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    This page was last modified February 5, 2000.