Bioenergetics Bioenergetics

Biochemical thermodynamics is the study of the energy changes in the biochemical reaction. • It concerned only with initial and final energy change not with the mechanism of reaction • Two types – Endergonic – Exergonic • In biological system endergonic and exergonic are coupled High energy compound

• Certain compound on hydrolysis give energy • Produce 7 cal/mole or more at pH- 7.0 • Generally contain phosphates so also called as high energy phosphate compounds • Classify in 5 groups – Pyrophosphates e.g. ATP – Acyl Phosphates e.g. 1,3 bisphosphoglycerate – Enol phosphates e.g. phosphoenol pyruvate – Thioesters e.g. acyl CoA – Phosphagenes e.g. phosphocreatine • High energy bond- On hydrolysis of acid anhydried bond of high energy compound provide free energy so these bonds are called high energy bonds • ATP-ADP cycle • ATP Synthesis- by 2 ways – Oxidative phosphorylation – Substrate level phosphorylation ▪ Adenylyl Kinase (Myokinase)- ATP+AMP 2ADP Storage forms of high energy phosphate • Phosphocreatine- in vertebrate • Phosphoarginine- in invertebrate • Provide source of energy Biological oxidation

• Oxidation which takes place in living system • Generated energy is conserved as ATP • Electron moves from more negative to more positive reduction potential Importance • Biological oxidation deals with the uses of respiratory O2 in the body • Several important biological oxidation reactions are directly associated with respiratory O2 •In the respiratory chain, O2 is used as final electron acceptor and reduced to water •Apart form respiratory chain, several enzymes use O2 as final electron acceptor and produce H20 2 •Respiratory O2 is also required for the removal of toxins and drugs from the body. •Superoxide ion derived from 02 function as microbicide • Biological oxidation provides means for the regeneration of coenzymes, which are used in metabolism

• It is the final aspect of all energy-producing compounds

• In myocardial infarction O2 supply to cardiac muscle is impaired. As a result of this, energy production in cardiac cells is blocked, which lead to necrosis

• In some instances like high altitudes, surgeries to maintain normal functioning of body or cells O2 supply is essential

• Though O2 is essential for survival of cells, at high concentration it is toxic to cells. Hence, it is used to treat tumours along with radiation Enzymes in biological oxidation

• Calssified in 4 groups – Oxidase – Dehydrogenase – Hydroperoxidase – oxygenase Oxidase

• Catalyze removal of H2 from substrate using O2 as hydrogen acceptor and form H2O or H2O2 e.g. cytochrome oxidase- consist od cyt a and a3, each subunit has fe and cu.onlya3 directly react with O2 L-amino acid oxidase- FMN linked xanthine oxidase- contains Mb Dehydrogenase

• Transfers H2 from one substrate to another but do not use O2 as hydrogen acceptor also called as anaerobic dehydrogenase e.g. NAD+ dependent- alcohol dehydrogenase NADP+ dependent- enoyl reductase FMN dependent- NADH dehydrogenase FAD dependent- succinate dehydrogenase cytochromes Hydroperoxidase

• catalyze breakdown of H2O2 which is produced in the body during reduction • of oxygen to water

• H2O2 or organic peroxide are substrate • 2 types – Peroxidase- reduce peroxides using electron acceptor. e.g. ascorbic acid, Ubiquinone

– Catalse- hemoprotein, destroys H2O2 formed by action of oxidase, present in liver, kidney, bone marrow and blood – Glutathion peroxidase- in RBC, contains selenium • Protect body from harmful peroxides Oxygenases

• Direct transfer and incorporation of O2 into substrate • This type of O2 utilization is cyanide insensitive (resistant) • Divide in 2 subgroups

– Dioxygense- add both O2 atoms to substrate so also called oxygen transferase e.g. L- tryptophan dioxygenase

– Monoxygenase (MFO)- only one atom of O2 is added to substrate and another is removed as water e.g. phenyl alanine hydroxilase, tryptophan hydroxylase Electron transport chain

• Final common pathway in aerobic cells by which electrons derived from various

substrates are transferred to O2 is respiratory cahin • Occurs in mitochondria Structural organisation of ETC • 5 different enzyme complex (I,II,III,IV and V) • Certain mobile electron carrier e.g. NADH, Coenzyme Q, cytochrome C, Fe-S protein and

O2 Ubiquinone

• lipid soluble benzoquinone with long isoprenoid side chain • constituent of mitochondrial lipids • only non-protein component of electron transport chain • transfers electrons from fixed flavoprotein to cytochrome • Can carry both proton and electron so play central role Cytochromes

• 3 classes (a, b, c) depending on type of heme and absorption spectrum • The cytochromes are b, c1 and c • components of electron transport chain • heme proteins • Cytochrome c is a peripheral protein • b and c1 are integral membrane proteins • involved in transfer of electrons from ubiquinone to cytochrome oxidase • three types of cytochrome b-- cyt b560, • cyt b562 and cyt b566 Cytochrome P450

• its complex with carbon monoxide absorbs light at 450 nm. • Cyt P450 directly interacts with oxygen • two types of cytochrome P450 dependent monooxygenases or hydroxylases 1. Microsomal cytochrome P450 hydroxylase • microsomes of liver • NADPH as hydrogen donor • involved in hydroxylation of several drugs • Sometimes hydroxylation converts prodrug to active drug 2. Mitochondrial cytochrome P450 hydroxylase • mitochondria of liver, adrenal cortex, testes, ovaries and kidneys • It requires NADPH, flavoproteins and iron-sulfur proteins • adrenal cortex -for hydroxylation of steroid hormones • liver - hydroxylation of bile acids • testes and ovaries - hydroxylation of steroid hormones • Kidneys - for hydroxylation of Vit D Iron- Sulphur Protein

• Iron and sulfur are present as clusters in proteins • Fe in association with organic Sulphur atom of Cystein residue in the protein • Iron and sulfur are present in equimolar amounts • participate in one electron transfer reactions • NADH-CoQ reductase contain 4 Fe4S4 centers per molecule of FMN • succinate-CoQ reductase has 2 Fe2 S2 centers • Adrenodoxin in adrenal cortex contain Fe2 S2 center Complex- I Complex- II

Complex- III Q- Cycle Complex- IV

Complex- V

Inhibitors/ Uncouplers

Mitocondrial Shuttles

• Reoxidation of cytosolic NADH requires shuttle mechanism – glycerol 3-phosphate shuttle • found in muscle Mitocondrial Shuttles

• malate-aspartate shuttle – heart and liver Mitocondrial Shuttles

• What is an ATP-ADP translocase? – transport protein allowing ATP to exit mitocondrion and ADP to enter – result in moving one negative charge out of matrix • decreases proton motive force Mitocondrial Shuttles

• Other mitocondrial transport proteins act as shuttles