1 / 24

Product stabilizations in hydrolysis

Product stabilizations in hydrolysis. Relief of electrostatic repulsion by charge separation Ionization Isomerization Resonance. ATP Provides Energy by Group Transfers, not by Simple Hydrolysis. Energy from group transfer Two step reaction Phosphoryl group transfer

gella
Download Presentation

Product stabilizations in hydrolysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Product stabilizations in hydrolysis • Relief of electrostatic repulsion by charge separation • Ionization • Isomerization • Resonance

  2. ATP Provides Energy by Group Transfers, not by Simple Hydrolysis • Energy from group transfer • Two step reaction • Phosphoryl group transfer • Phosphoryl group displacement • Energy directly from ATP hydrolysis • Hydrolysis of bound ATP (GTP)  protein conformational change  mechanical motion, activity transition (active  inactive) • Muscle contraction, movement of enzymes along DNA, movement of ribosome along mRNA, helicase, GTP-binding proteins

  3. Phosphate Compounds • Phosphate compounds in living organisms • High-energy compounds : DG’o : <-25 kJ/mol • ATP: DG’o = -30.5 kJ/mol • Low-energy compounds : DG’o : >-25 kJ/mol • Glucose-6-phosphate: DG’o = -13.8 kJ/mol • Flow of phosphoryl group • From a compound with high phosphoryl group transfer potential to low potential • (1) PEP + H2O  pyruvate + Pi ; DG’o = -61.9 kJ/mol • (2) ADP + Pi  ATP + H2O ; DG’o = +30.5 kJ/mol • Sum: PEP + ADP  pyruvate + ATP ; DG’o = -31.4 kJ/mol

  4. Nucleophilic Displacement Reactions of ATP • Reactions of ATP • SN2 nucleophilic displacements • Nucleophiles; O of alcohol or carboxylate/ N of creatine, Arg, His • Nucleophilic attacks of the three phosphates • a-b phosphoanhydride bond has a higher energy (~46 kJ/mol) than b-g (~31 kJ/mol) • PPi 2 Pi by inorganic phosphatase DG’o = -19 kJ/mol further energy “push” for the adenylylation reaction

  5. Nucleophilic Displacement Reactions of ATP • Energy-coupling mechanism via adenylylation reaction

  6. Bioluminescence of Firefly • Conversion of chemical energy to light energy using ATP

  7. Assembly of Informational Macromolecules Requires Energy • DNA or RNA synthesis • NTP  release of PPi and hydrolysis to 2 Pi • Protein synthesis • Activation of amino acid by adenylylation

  8. ATP Energizes Active Transport and Muscle Contraction • ATP for molecular transport • 2/3 of the energy at rest is used for Na+/K+ pump in human kidney and brain • Contraction of skeletal muscle • ATP hydrolysis in myosin head • Movement along the actin filament

  9. Transphosphorylation Between Nucleotides • NTPs and dNTPs • Energetically equivalent to ATP • Generation from ATP • Nucleoside diphosphate kinase • ATP + NDP (or dNDP) ADP + NTP (or dNTP) • DG’o ≈ 0 • Driven by high [ATP]/[ADP] • Ping-pong mechanism

  10. Transphosphorylation Between Nucleotides • Adenylate kinase • 2ADP ATP + AMP, DG’o ≈ 0 • Under high ATP demanding conditions • Creatin kinase • ADP + PCr ATP + Cr, DG’o = -12.5kJ/mol • PCr : Phosphoryl reservoir for high ATP demanding conditions in muscle, brain, and kidney • Inorganic Polyphosphate (PolyP) as a Phosphate Group Donor • PolyP • Polymer of phosphate • Phosphagen: reservoir of phosphoryl groups • In prokaryotes • PolyP kinase-1 : synthesis of polyP • ATP + polyPn ADP + polyPn+1 • PolyP kinase-2 : synthesis of GTP or ATP • GDP + polyPn+1 GTP + polyPn

  11. 13.3 Biological Oxidation-Reduction Reactions

  12. Electron flow can do biological work • Electromotive force (emf) • Force proportional to the difference in electron affinity between two species  “Do work” • Glucose (e- source)  sequential enzymatic oxidation  e- release Flow e- via e- carriers  O2 • e.g. generation of proton motive force in mitochondria to generate ATP emf; provide energy for biological works

  13. Oxidation States of C in the Biosphere • Oxidation state of C • Number of electrons owned by C • depends on electronegativity of bonding atoms • O> N> S> C> H • In biological system; biological oxidation = dehydrogenation

  14. Biological Oxidation Often Involve Dehydrogenation • 4 ways for electron transfer • Direct electron transfer via redox pairs Fe2+ + Cu2+ Fe3+ + Cu+ • Transfer of hydrogen atoms AH2 A + 2e- + 2H+ AH2 + B  A + BH2 • Transfer of hydride ion (:H-) • Direct combination with O2 R-CH3 + 1/2O2 R-CH2-OH • Reducing equivalent • A single e- equivalent participating in an oxidation-reduction reaction • Biological oxidation • Transfer of two reducing equivalents

  15. Reduction Potential measures for e- affinity • Standard reduction potential, Eo • A measure of affinity of electron • Measurement of Eo • Standard reference half reaction (hydrogen electrode) H+ + e- 1/2H2 ,Eo = 0 V • Connection of the hydrogen electrode to another half cell (1M of oxidant and reductant, 101.3 kPa) • The half cell with the stronger tendency to acquire electrons : positive Eo • Reduction potential E • E = Eo + RT/nF ln [e- acceptor]/[e- donor] • n: the number of e- transferred/molecule • F; Faraday constant • E = Eo + 0.026V/n ln [e- acceptor]/[e- donor] at 298K • Standard reduction potential at pH 7.0, E’o

  16. Standard Reduction Potentials

  17. Free Energy Change For Oxidation Reduction Reaction • Oxidation-reduction reaction • The direction of e- flow ; to the half-cell with more positive E • DG = -nFDE or DG’o = -nFDE’o • Calculation of DG • Standard conditions, pH 7, 1M of each components • (1) Acetaldehyde + 2H+ + 2e- ethanol, E’o = -0.197 V • (2) NAD+ + 2H+ + 2e-  NADH + H+, E’o =-0.320 V • (1) - (2) = Acetaldehyde + NADH + H+  ethanol + NAD+ • DE’o =E’o of e- acceptor - E’o ofe- donor = -0.197 V - (-0.320 V) = 0.123 V • DG’o =-2 (96.5 kJ/V mol)(0.123V) = -23.7 kJ/mol • 1 M acetaldehyde and NADH, 0.1M ethanol and NAD+ • Eacetaldehyde =E’o +RT/nF ln [acetaldehyde]/[ethanol] = -0.197 V + 0.026 V/2 ln 1/0.1 = -0.167 V • ENADH =E’o +RT/nF ln [NAD+]/[NADH] = -0.320 V + 0.026 V/2 ln 1/0.1 = -0.350 V • DE = -0.167 V - (-0.350 V) = 0.183 V • DG = -2 (96.5 kJ/V mol)(0.183V) = -35.3 kJ/mol

  18. e- carriers • Complete oxidation of glucose • C6H12O6 + 6O2 6 CO2 + 6 H2O • DG’o = -2,840 kJ/mol • e- removed in oxidation steps are transferred to e- carriers • Electron carriers • NAD+, NADP+ : soluble carrier • FMN, FAD : prosthetic group of flavoproteins • Quinones (ubiquinone, plastoquinone) : membrane • Iron-sulfur proteins, cytochromes : cytosol or membrane

  19. NADH and NADPH • NAD(P) • Nicotinamide adenine dinucleotide (phosphate) • Accept hydride (:H-) released from oxidation (dehydrogenation) of substrate : either A side or B side, not both sides • NAD(P)+ + 2H+ + 2e- NADH + H+ • NAD(P)+ : + indicates oxidized form, not the net charge of NAD(P)which is - Benzenoid ring Quinonoid ring

  20. Metabolic Roles of NADH and NADPH • Metabolic Roles of NADH and NADPH • NADH • Functions in oxidations in catabolic reactions (NAD+ >NADH) • NADPH • Functions in reductions in anabolic reactions (NADPH > NADP+ ) • Oxidoreductases or dehydrogenases • Specific preference to NAD or NADP • Spatial segregation • Oxidation of fuels in mitochondria • Biosynthesis in cytosol • AH2 + NAD+  A +NADH + H+ • Alcohol dehydrogenase • CH3CH2OH + NAD+  CH3CHO +NADH + H+ • A +NADPH + H+  AH2 + NADP+ • Rossmann fold • NAD or NADP binding domain • Relatively loose binding  diffusion to other enzyme

  21. Dietary Deficiency of Niacin: Pellagra • Niacin (nicotinic acid) • Source of the pyridine-like ring of NAD and NADP • Low amount of synthesis from Trpin human • Pellagra (rough skin) • Disease from niacin deficiency • Can be cured by niacin or nicotinamide, not by nicotine

  22. Flavin Nucleotide • Flavin nucleotides • FMN : flavin mononucleotide • FAD: falvin adenine dinucleotide • Derived from riboflavin • One or two electron transfer • Flavoproteins • Enzymes catalyzing oxidation-reduction reactions using FMN or FAD as coenzyme • Tight-bound flavin nucleotides • Different E’o from that of free flavin nucleotide • FAD in succinate dehydrogenase : E’o = 0 V • Free FAD : E’o = -0.219 V • Some contains additional tightly bound inorganic ions (Fe or Mo) • c.f. Cryptochromes • Flavoproteins mediating the blue light effect in plant and controlling circadian rhythms in mammals

  23. Flavin Nucleotide 450nm absorption 360nm absorption 370 and 440 nm absorption

  24. Enzymes with Electron Carriers

More Related