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Fig. 2. | BMC Biology

Fig. 2.

From: Organelle acidification: an ancient cellular leak detector

Fig. 2.

Distribution and orientation of rotary-motor proton pumps across the three domains of life. Archaeal A-ATPases and bacterial (including cyanobacterial) F-ATPases use the flow of protons into the cytoplasm to convert ADP to ATP. This is balanced by an energy-dependent outward flow driven by the electron transport chain. Eukaryotic mitochondria and chloroplasts are endosymbiotic descendants of alpha-proteobacteria and cyanobacteria, and continue to use F-ATPases like their free-living ancestors. Eukaryotic V-ATPases are derived from archaeal ATPases but run in the opposite direction: they hydrolyse ATP to drive protons into the extracellular environment, the organellar lumen, or sealed extracellular pockets. The flow of protons out of the cytoplasm is balanced by an inward flow via various symporters and antiporters. The flow of protons into endosomes and extracellular pockets is unbalanced, leading to their acidification (pink). OM outer membrane, PM plasma membrane, TM thylakoid membrane

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