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In most cases the proton-motive force is generated by an electron transport chain which acts as a proton pump, using the Gibbs free energy of redox reactions to pump protons (hydrogen ions) out across the membrane, separating the charge across the membrane. In mitochondria, energy released by the electron transport chain is used to move protons ...
The result is the disappearance of a proton from the cytoplasm and the appearance of a proton in the periplasm. Mitochondrial Complex III is this second type of proton pump, which is mediated by a quinone (the Q cycle). Some dehydrogenases are proton pumps, while others are not. Most oxidases and reductases are proton pumps, but some are not.
This energy is supplied by consuming proton motive force to drive electrons in a reverse direction through an electron transport chain and is thus the reverse process as forward electron transport. In some cases, the energy consumed in reverse electron transport is five times greater than energy gained from the forward process. [ 1 ]
This transport chain produces a proton-motive force, pumping H + ions across the membrane and producing a concentration gradient that can be used to power ATP synthase during chemiosmosis. This pathway is known as cyclic photophosphorylation, and it produces neither O 2 nor NADPH.
The proton motive force and ATP production can be maintained by intracellular acidosis. [88] Cytosolic protons that have accumulated with ATP hydrolysis and lactic acidosis can freely diffuse across the mitochondrial outer-membrane and acidify the inter-membrane space, hence directly contributing to the proton motive force and ATP production.
The phosphate carrier (PiC) mediates the electroneutral exchange of phosphate (H 2 PO − 4; P i) for OH − or symport of phosphate and protons (H +) across the inner membrane, and the driving force for moving phosphate ions into the mitochondria is the proton motive force.
The overall structure and the catalytic mechanism of the chloroplast ATP synthase are almost the same as those of the bacterial enzyme. However, in chloroplasts, the proton motive force is generated not by respiratory electron transport chain but by primary photosynthetic proteins. The synthase has a 40-aa insert in the gamma-subunit to inhibit ...
Structure of the human uncoupling protein UCP1. An uncoupling protein (UCP) is a mitochondrial inner membrane protein that is a regulated proton channel or transporter.An uncoupling protein is thus capable of dissipating the proton gradient generated by NADH-powered pumping of protons from the mitochondrial matrix to the mitochondrial intermembrane space.