Stroma proton return

Flow of Electrons from H20 to NADP+ Drives Proton Transport into the Thylakoid Lumen Protons Return to the Stroma through an ATP-Synthase Carbon Fixation Utilizes the Reductive Pentose Cycle Ribulose-Bisphosphate Carboxylase-Oxygenase Photorespiration and the C-4 Cycle... 

NADP+ reduced to NADPH. (Two protons are taken up when the flavoprotein is reduced by photosystem I one ends up on NADPH, and the other is returned to the solution.) The flow of protons from the thylakoid lumen back to the stroma through an ATP-synthase (CF0-CF ) drives the formation of ATP. The abbreviations used in this figure are the same as in figure 15.17. 

The protons, now at 1,000-fold higher concentration in the thylakoid lumen than in the surrounding stroma, return across the thylakoid membrane from lumen to stroma and produce the chemical energy ATP by means of the protein-based machine ATP synthase, briefly considered below and in some detail in Chapter 8. 

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