In bacteria and ATP-producing organelles other than mitochondria, reducing equivalents provided by electron transfer or photosynthesis power the translocation of protons. This process effectively couples the translocation of protons to the mechanical motion between the Loose, Tight, and Open states of F 1 necessary to phosphorylate ADP. This series of conformational changes, channeled through the a and b subunits of the F O particle, drives a series of conformational changes in the stalk connecting the F O to the F 1 subunit. Protons translocate across the inner mitochondrial membrane via proton wire. The F oF 1 ATP synthase of mitochondria, in contrast, usually conduct protons from high to low concentration across the membrane while drawing energy from this flow to synthesize ATP. ATP itself powers this transport in the plasma membrane proton ATPase and in the ATPase proton pumps of other cellular membranes. For example, the translocation of protons by cytochrome c oxidase is powered by reducing equivalents provided by reduced cytochrome c. In mitochondria, reducing equivalents provided by electron transfer or photosynthesis power this translocation of protons. It is found in the mitochondrial inner membrane where it functions as a proton transport-driven ATP synthase. The F-type proton ATPase is a multi-subunit enzyme of the F-type (also referred to as ATP synthase or F OF 1 ATPase). The energy required for the proton pumping reaction may come from light (light energy bacteriorhodopsins), electron transfer (electrical energy electron transport complexes I, III and IV) or energy-rich metabolites (chemical energy) such as pyrophosphate (PPi proton-pumping pyrophosphatase) or adenosine triphosphate (ATP proton ATPases). The proton pump does not create energy, but forms a gradient that stores energy for later use. The process could also be seen as analogous to cycling uphill or charging a battery for later use, as it produces potential energy. The difference in pH and electric charge (ignoring differences in buffer capacity) creates an electrochemical potential difference that works similar to that of a battery or energy storing unit for the cell. It is an active pump that generates a proton concentration gradient across the inner mitochondrial membrane because there are more protons outside the matrix than inside. In cell respiration, the proton pump uses energy to transport protons from the matrix of the mitochondrion to the inter-membrane space. An electrochemical gradient represents a store of energy ( potential energy) that can be used to drive a multitude of biological processes such as ATP synthesis, nutrient uptake and action potential formation. The combined transmembrane gradient of protons and charges created by proton pumps is called an electrochemical gradient. An example of a proton pump that is not electrogenic, is the proton/potassium pump of the gastric mucosa which catalyzes a balanced exchange of protons and potassium ions. Proton transport becomes electrogenic if not neutralized electrically by transport of either a corresponding negative charge in the same direction or a corresponding positive charge in the opposite direction. it generates an electric field across the membrane also called the membrane potential. Transport of the positively charged proton is typically electrogenic, i.e. Proton pumps are divided into different major classes of pumps that use different sources of energy, have different polypeptide compositions and evolutionary origins. Thus, not only throughout nature but also within single cells, different proton pumps that are evolutionarily unrelated can be found. Mechanisms are based on energy-induced conformational changes of the protein structure or on the Q cycle.ĭuring evolution, proton pumps have arisen independently on multiple occasions. Proton pumps catalyze the following reaction: For generators of proton beams, see synchrotron and cyclotron.Ī proton pump is an integral membrane protein pump that builds up a proton gradient across a biological membrane. This article is about biochemical proton pumps.
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