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ATP Synthase - Molecular Biochemistry I F1Fo ATP Synthase...

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F 1 Fo ATP Synthase Copyright © 1999-2007 by Joyce J. Diwan. All rights reserved. Molecular Biochemistry I
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F1Fo ATP Synthase of mitochondria, chloroplasts, bacteria: When the electrochemical H+ gradient is favorable, F1Fo catalyzes ATP synthesis coupled to spontaneous H+ flux toward the side of the membrane where F1 protrudes (e.g., toward the mitochondrial matrix). ADP + P i ATP F 1 F o 3 H + matrix intermembrane space ATP synthesis with pH & ∆Ψ - - - + + +
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If no pH or ∆ Ψ exists to drive the forward reaction, K eq favors the reverse, ATP hydrolysis (ATPase). In some bacteria , the reverse reaction has a physiological role, providing a mechanism for ATP-dependent creation of a proton gradient that drives other reactions. ADP + P i ATP F 1 F o 3 H + ATPase with H + gradient dissipated matrix intermembrane space ADP + P i ATP F 1 F o 3 H + matrix intermembrane space ATP synthesis with pH & ∆Ψ - - - + + +
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Inhibitors of F1Fo, that block H+ transport coupled to ATP synthesis or hydrolysis, include: w oligomycin , an antibiotic w DCCD (dicyclohexylcarbodiimide), a reagent that reacts with carboxyl groups in hydrophobic environments, forming a covalent adduct.
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Roles of major subunits were determined in studies of submitochondrial particles ( SMP ). In mitochondria treated with ultrasound , inner membrane breaks & reseals as vesicles, with F1 on the outer surface. Since F1 of intact mitochondria faces the matrix, these SMP are said to be inside out . By EM with negative stain, ATP Synthase appeared as " lollipops " on the inner mitochondrial membrane, facing the matrix. Higher resolution cryo-EM later showed each lollipop to have 2 stalks . See Movie. mitochondrion ultrasound SMP F 1
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w After removal of F1 , the SMP membrane containing Fo is leaky to H+ . Adding back F1 restores normal low permeability to H+. Thus it was established that Fo includes a “ H+ channel ." w F1 , the lollipop head , when extracted from SMP, catalyzes ATP hydrolysis (spontaneous reaction in the absence of an energy input). Thus F1 contains the catalytic domain(s). mitochondrion ultrasound SMP F 1
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w Either oligomycin or DCCD blocks the H+ leak in membranes depleted of F 1 . Thus oligomycin & DCCD inhibit the ATP Synthase by interacting with Fo . ATP synthase complexes of bacteria, mitochondria & chloroplasts are very similar, with only minor differences. ADP + P i ATP F 1 F o 3 H + matrix intermembrane space ATP synthesis with pH & ∆Ψ - - - + + +
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Mitochondria are believed to have evolved from symbiotic aerobic bacteria ingested by an anaerobic host cell. The limiting membrane of the bacterium became the inner mitochondrial membrane . Mitochondria contain a small DNA chromosome, but genes that encode most mitochondrial proteins are in the nucleus, consistent with transfer of some DNA during evolution. aerobic bacterium protoeukaryotic cell lacking aerobic metabolism DNA mitochondrial precursor nucleus
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Looking down at the membrane, α & β subunits alternate around a ring ( γ to be discussed later.) The subunit composition of the ATP Synthase was first established for E. coli , which has an operon that encodes genes for all subunits.
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