OXIDATIVE PHOSPHORYLATION
Updated 04-May-2020.
Mondo shtuff from around the internet, all about OXIDATIVE PHOSPHORYLATION!
A New Concept for Energy Coupling in Oxidative Phosphorylation Based on a Molecular Explanation of the Oxygen Exchange Reactions: The Pi ⇄ HOH exchange reaction of oxidative phosphorylation is considerably less sensitive to uncouplers than the Pi ⇄ ATP and ATP ⇄ HOH exchanges. The uncoupler-insensitive Pi ⇄ HOH exchange is inhibited by oligomycin. These results and other considerations suggest that the relatively rapid and uncoupler-insensitive Pi ⇄ HOH exchange results from a rapid, reversible hydrolysis of a tightly but noncovalently bound ATP at a catalytic site for oxidative phosphorylation, concomitant with interchange of medium and bound Pi. Such tightly bound ATP has been demonstrated in submitochondrial particles in the presence of uncouplers, Pi, and ADP, by rapid labeling from 32Pi under essentially steady-state phosphorylation conditions. These results lead to the working hypothesis that in oxidative phosphorylation energy from electron transport causes release of preformed ATP from the catalytic site. This release could logically involve energy-requiring protein conformational change.
Partial Resolution of the Enzymes Catalyzing Oxidative Phosphorylation: Maynard E. Pullman, Harvey S. Penefsky, Anima Datta, E. Racker
Chemiosmotic Hypothesis of Oxidative Phosphorylation: Dr. Moyle and Dr. Mitchell answer criticisms of their interpretation of tests of the hypothesis proposed by Dr. Mitchell in 1961 to explain ATP synthesis in the inner membrane of mitochondria and of chloroplasts by a fuel-cell type of mechanism
My botty best at summarizing from Wikipedia: in most eukaryotes, this takes place inside mitochondria . adenosine triphosphate (ATP) is produced by oxidizing molecular oxygen . the energy of the double bond of oxygen is redox reactions release the energy stored in the relatively weak double bond of O2, which is used to form ATP . in eukaryotes, a series of protein complexes are catalyzed by store of energy tapped when protons flow back across membrane and down energy gradient . enzyme transforms ADP into adenosine triphosphate, in phosphorylation reaction . reaction driven by proton flow, enzymes carrying out metabolic pathway are target of many drugs and poisons that inhibit their activities . it is the terminal process of cellular respiration in eukaryotes and accounts for high ATP yield . energy is transferred the movement of protons creates an electrochemical gradient across the membrane . it has two components: a difference in proton concentration and electric potential . ATP synthase releases stored energy by completing the circuit . in the case of the fusobacterium Propionigenium modestum it drives the counter-rotation of subunits a and c . the amount of energy released by oxidative phosphorylation is high electrons are transferred within the intermembrane space by the water-soluble electron transfer protein cytochrome c . this carries only electrons, and these are transferred by the reduction and oxidation of an iron some bacterial electron transport chains use different quinones, such as menaquinone . there are several types of iron–sulfur clusters . metal ion cofactors undergo redox reactions without binding or releasing protons . they serve solely to transport electrons through proteins . electrons move quite long distances through protein by hopping along chains of electrons are removed from NADH and passed to oxygen through a series of enzymes that each release a small amount of the energy . in eukaryotes, the enzymes pump protons across the inner membrane of the mitochondrion is present in almost all eukaryotes . complex I is a giant enzyme with a molecular mass of about 1,000 kilodaltons (kDa) the the reaction that is catalyzed by this enzyme is the two electron oxidation of NADH by coenzyme Q10 or ubiquinone . the electrons enter complex I via a prosthetic group four protons are pumped from the matrix into the intermembrane space . electrons are transferred from chain of iron–sulfur clusters to ubiquinone molecule . two protons taken up from complex II is the only enzyme that is part of both the citric acid cycle and the electron transport chain . it oxidizes succinate to fumarate and reduces ubiquinone . complex II does not transport complex II is an enzyme that accepts electrons from electron-transferring flavoprotein . it uses these electrons to reduce ubiquinone . the enzyme attaches to the surface of the membrane . in mammals, this enzyme is a dimer, with each subunit complex containing 11 protein subunits . in plants, ETF-Q oxidoreductase is also important in the metabolic responses that allow reaction catalyzed by complex III is the oxidation of one molecule of ubiquinol . reaction is the reduction of two molecules of cytochrome c, a heme protein . the first two substrates are released, but this ubisemiquinone intermediate remains bound . the rather complex two-step mechanism by which this occurs is important . it increases the efficiency of proton transfer . the mammalian enzyme has 13 subunits, two heme groups and multiple metal ion cofactors . it transfers electrons to oxygen and hydrogen (protons) while pumping protons across the membrane alternative oxidase transfers electrons directly from ubiquinol to oxygen . alternative pathways might enhance resistance to injury, by reducing oxidative stress . recent data suggest that the complexes might form higher-order structures called supercomplexes or “respirasomes” in this model, the complex exist as organized sets of interacting enzymes . debate over this bacteria and archaea use many different substances to donate or accept electrons . prokaryotes can grow under a wide variety of environmental conditions . oxidative phosphorylation can be driven by a large midpoint potential measures how much energy is released when chemical is oxidized or reduced . reducing agents have negative potentials and oxidizing agents have positive potentials . out of these compounds, the succinate/fuma prokaryotes use redox pairs that have only a small difference in midpoint potential . small amount of energy released in this reaction is enough to pump protons and generate ATP . this problem is solved by using prokaryotes also possess a range of isozymes – different enzymes that catalyze the same reaction . in E. coli, there are two different types of ubiquinol oxida oxidase transfers only one proton per electron, but has high affinity for oxygen . enzyme drives synthesis of ATP from ADP and phosphate (Pi) estimates of number of protons required to synthe ATP synthase reaction runs from right to left, hydrolyzing ATP and pumping protons across membrane . when proton-motive force is high, reaction proceeds from left to right, turning ADP into the stalk and the ball-shaped headpiece is called F1 and is the site of ATP synthesis . both the and subunits bind nucleotides, but only the . subunit rotation might be caused by changes in the ionization of amino acids . rotating ring drives the rotation of the central axle within the and subunits . in some bacteria and archaea, ATP synthesis is driven by the movement of sodium ions through the cell membrane . this is not always the case . archaea such as Methanococcus also contain the A1Ao synthase . it is possible that, in some species, the enzyme is a specialized sodium-driven enzyme . but this might transfer of four electrons and four protons reduces oxygen to water, which is harmless . transfer of one or two electrons produces superoxide or peroxide anions, which are dangerously reactive . reactive oxygen species are proton-pumping complexes can lead to electron “leakage” when electrons transfer to oxygen . mitochondria regulate their activity to balance ATP production against oxidant generation . proton motive force and ATP oligomycin inhibits ATP synthase, protons cannot pass back into mitochondrion . many site specific inhibitors of ETC have contributed in the present knowledge of mitochondrial respiration . fish poison rotenone, barbitutate drug amytal and antibiotic piercidin A inhibit NADH and coenzyme Q. in brown adipose tissue, regulated proton channels can uncouple respiration from ATP synthesis . mechanism by which ATP is generated remained mysterious for another 20 years . scientists searching for an the chemiosmotic theory was solved by Peter D. Mitchell in 1961 . at first, this proposal was highly controversial, but it was slowly accepted . Lehninger Principles of Biochemistry (4th ed.). W. H. Freeman. ISBN 0-7167-4339-6. Schneider ED; Sagan D (2006). Into the Cool: Energy ISBN 0-226-73937-6. Lane N (2006). Power, Sex, Suicide: Mitochondria and the Meaning of Life (1st ed.). Oxford University Press, USA. Bioenergetics 3 (1st ed.). Academic Press. ISBN 0-12-518121-3. Haynie D (2001). ISBN 0-521-79549-4. Rajan SS (2003). Introduction to Bioenergetics (1st ed.). ISBN 81-261-1364-2. ISBN 81-161-1363-2.