CHAPTER 10B

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ATP Synthesis Continued F 1 unit has five subunits: a 3 , b 3 , g , d , and e F 0 unit has three subunits: a, b 2 , and c 12 F 0 motor converts the proton motive force into the rotational force of the central shaft ( e and g subunits) that in turn, drives ATP synthesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.14 The ATP Synthase From Escherichia coli Section 10.2: Oxidative Phosphorylation

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ATP Synthesis Continued b subunits of the ATP synthase have three conformations: open (O), tight (T), and loose (L) Steps: 1. ADP and P i binds to L site; rotation converts it to T conformation 2. ATP synthesized 3. Rotation converts T site to O site, releasing ATP From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.15 ATP Synthesis Model Section 10.2: Oxidative Phosphorylation

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Control of Oxidative Phosphorylation Activated when ADP ( respiratory control ) and P i concentrations are high Inhibited when ATP concentrations are high From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.16 The ADP-ATP Translocator and the Phosphate Translocase Section 10.2: Oxidative Phosphorylation

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Control of Oxidative Phosphorylation Cont. Amounts of ATP and ADP in mitochondria are controlled by the ADP-ATP translocator Amount of H 2 PO 4 - is controlled by phosphate carrier (H 2 PO 4 - /H + symporter ) From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.16 The ADP-ATP Translocator and the Phosphate Translocase Section 10.2: Oxidative Phosphorylation

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The Complete Oxidation of Glucose Two mechanisms to move electrons from cytoplasmic NADH, derived from glycolysis, into the mitochondrial ETC are glycerol phosphate shuttle and malate-aspartate shuttle From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.17a Shuttle Mechanisms That Transfer Electrons from Cytoplasmic NADH to the Respiratory Chain Section 10.2: Oxidative Phosphorylation

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The Complete Oxidation of Glucose Continued The glycerol phosphate shuttle uses cytoplasmic NADH (glycolytic pathway) to reduce DHAP into glycerol-3-phosphate, which can enter the intermembrane space From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.17a Shuttle Mechanisms That Transfer Electrons from Cytoplasmic NADH to the Respiratory Chain Section 10.2: Oxidative Phosphorylation

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Section 10.2: Oxidative Phosphorylation Figure 10.17b Shuttle Mechanisms That Transfer Electrons from Cytoplasmic NADH to the Respiratory Chain The Complete Oxidation of Glucose Continued The malate -aspartate shuttle is used to transfer electrons from cytoplasmic NADH (glycolytic pathway) to the mitochondrial ETC This is the more efficient of the two mechanisms

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Section 10.2: Oxidative Phosphorylation The Complete Oxidation of Glucose Continued Cytoplasmic NADH reduces oxaloacetate to malate , which is transported to the matrix Malate is reoxidized to produce NADH Figure 10.17 Shuttle Mechanisms That Transfer Electrons from Cytoplasmic NADH to the Respiratory Chain

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Section 10.2: Oxidative Phosphorylation

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press All living processes take place within a redox environment Redox state is regulated within a narrow range because of redox-sensitive nature of many pathways Important linked redox pairs (NAD(P)H/NAD(P) + and GSH/GSSG) help maintain redox conditions GSH (glutathione) is a key, cellular-reducing agent Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Oxygen usage comes with the danger of forming reactive oxygen species ( ROS ) Some ROS act as signaling molecules Antioxidants interact with ROS to mitigate damage Under certain conditions, antioxidant mechanisms are overwhelmed, leading to oxidative stress Oxidative damage has been linked to 100 human diseases Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactive Oxygen Species Properties of oxygen related to its structure Diatomic oxygen is a diradical , meaning it has two unpaired electrons Figure 10.18 Overview of Oxidative Phosphorylation and ROS Formation in the Mitochondrion Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactive Oxygen Species Continued Oxygen can only accept one electron at a time Electrons can leak out of the ETC and interact with O 2 Figure 10.18 Overview of Oxidative Phosphorylation and ROS Formation in the Mitochondrion Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Types of reactive oxygen species: First created is superoxide radical (O 2 ● - ), which acts as a nucleophile O 2 ● - can react with itself to form hydrogen peroxide H 2 O 2 H 2 O 2 can react with Fe 2+ to form hydroxyl radical ( ● OH), which can initiate autocatalytic radical chain reaction Figure 10.19 Radical Chain Reaction Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Singlet oxygen ( 1 O 2 ) formed from H 2 O 2 or superoxide can be damaging to aromatics and conjugated alkenes Section 10.3: Oxygen , Cell Function, and Oxidative Stress Figure 10.19 Radical Chain Reaction

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press There are also reactive nitrogen species ( RNS ) Nitric oxide, nitrogen dioxide, and peroxynitrite are important examples Nitric oxide ( ● NO) is an important signaling molecule Physiological functions of NO include blood pressure regulation, inhibition of blood clotting, and destruction of foreign cells by macrophages Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.20 The Respiratory Burst Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactive oxygen species also generated for the respiratory burst Macrophages and neutrophils actively make large quantities of ROS Use ROS in order to destroy microorganisms and damaged cells Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Antioxidant Enzyme Systems To protect against oxidative stress, living organisms have developed several antioxidant defense mechanisms Major enzymatic defenses are provided by four enzymes: superoxide dismutase, glutathione peroxidase, peroxiredoxin , and catalase Superoxide dismutase forms H 2 O 2 and O 2 from superoxide radical Catalase forms H 2 O and O 2 from H 2 O 2 Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Antioxidant Enzyme Systems Continued Glutathione peroxidase uses the reducing agent GSH to control peroxide levels Reduces H 2 O 2 to form water and transforms organic peroxides to alcohols Glutathione reductase is also an important enzyme in the glutathione system Figure 10.21 The Glutathione-Centered System Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Antioxidant Enzyme Systems Continued Peroxiredoxins (PRX) are a class of enzymes that detoxify peroxides Uses thiol -containing peptides like thioredoxin Thioredoxin is involved in redox reactions mediated by the peroxiredoxin / thioreductase system Figure 10.22 The Thioredoxin-Centered System Section 10.3: Oxygen , Cell Function, and Oxidative Stress

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Section 10.3: Oxygen , Cell Function, and Oxidative Stress From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Antioxidant Molecules Organisms use antioxidant molecules to protect themselves from radicals a - Tocopherol (vitamin E) is a potent, lipid-soluble radical scavenger Figure 10.23 Selected Antioxidant Molecules

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Section 10.3: Oxygen , Cell Function, and Oxidative Stress From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Antioxidant Molecules Continued b -carotene , a carotenoid , is a precursor of vitamin A (retinol): a potent, lipid-soluble radical scavenger in membranes Figure 10.23 Selected Antioxidant Molecules

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Section 10.3: Oxygen , Cell Function, and Oxidative Stress From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Antioxidant Molecules Continued Ascorbate protects membranes through two mechanisms: scavenging a variety of ROS in aqueous environments and enhancing the activity of a - tocopherol Figure 10.24 Regeneration of a -Tocopherol by L -ascorbate