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Reverse electron flow
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<p>Reverse electron flow (also known as reverse electron transport) is a mechanism in <a href="/facts/Microbial_metabolism/mnzhpwaK">microbial metabolism</a>. <a href="/facts/Chemolithotroph/1CboHMzX">Chemolithotrophs</a> using an <a href="/facts/Electron_donor/7JxwwW43">electron donor</a> with a higher <a href="/facts/Redox_potential/PqpNUgSl">redox potential</a> than <a href="/facts/NADP/XMgmPQ5t">NAD(P)+/NAD(P)H</a>, such as nitrite or sulfur compounds, must use energy to reduce NAD(P)+. This energy is supplied by consuming <a href="/facts/Proton_motive_force/2clDS3bT">proton motive force</a> to drive electrons in a reverse direction through an <a href="/facts/Electron_transport_chain/QjcIkgeR">electron transport chain</a> 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. <a href="/facts/Autotroph/UDc8bzqD">Autotrophs</a> can use this process to supply reducing power for inorganic <a href="/facts/Carbon_fixation/JqvfmCdH">carbon fixation</a>. </p><p>Reverse electron transfer (RET) is the process that can occur in respiring <a href="/facts/Mitochondria/ErHqrdJ1">mitochondria</a>, when a small fraction of electrons from <a href="/facts/Redox/Pyd5RVcj">reduced</a> <a href="/facts/Ubiquinol/tUfSbf5I">ubiquinol</a> is driven upstream by the <a href="/facts/Membrane_potential/DpNG14c7">membrane potential</a> towards <a href="/facts/Mitochondrial_complex_I/Vn8Lf26t">mitochondrial complex I</a>. This results in <a href="/facts/Redox/Pyd5RVcj">reduction</a> of <a href="/facts/Oxidized/Pyd5RVcj">oxidized</a> <a href="/facts/Pyridine/X817hCch">pyridine</a> nucleotide (<a href="/facts/Nicotinamide_adenine_dinucleotide/BHdLW925">NAD</a>+ or <a href="/facts/NADP/XMgmPQ5t">NADP</a>+). This is a reversal of the <a href="/facts/Exergonic/2kPJobE7">exergonic</a> reaction of forward <a href="/facts/Electron_transfer/BIdASS9R">electron transfer</a> in the mitochondrial complex I when electrons travel from <a href="/facts/NADH/BHdLW925">NADH</a> to <a href="/facts/Ubiquinone/xoeh3R3e">ubiquinone</a>. </p>