Biological
Oxidation
Dr. N. Guha Niyogi
Asstt Professor, Biochemistry, GGMC
Ist MBBS Biochemistry
31/10/22
• Stages of oxidation
• Biological oxidation
Specific • Electron transport chain
• Oxidative phosphorylation
Learning • Regulation of oxidative phosphorylation
Objectives •
•
Inhibitors of ETC
Uncouplers of ETC
• Inophores
• Biomedical importance
Mitochondria
Few Definitions…….
• Oxidation : Removal of electrons.
• Reduction : Gain of electrons.
• Respiration : Inspiration and Expiration
Higher animals is dependent upon a steady supply of oxygen .
Aerobic vs Anaerobic organisms
• Capture a far greater proportion of the available free energy of respiratory substrates
• Mitochondria :“powerhouses” of the cell.
• Redox couple Pair of a substance that exists both in the reduced state and in the oxidized state,
• Electron Transport Chain and Biological oxidation : Transfer of electron from “food” to the
reduced coenzyme through the respiratory chain finally to molecular oxygen .
• Oxidative phosphorylation : Coupling of oxidation with Respiration to the generation of the high-
energy intermediate ATP.
Reducing Equivalents and Biological oxidation
Stages of • First phase - Primary metabolism
• Second phase - Secondary metabolism
Oxidation of • Third phase - Tertiary metabolism
•
Foodstuff
Enzymes of • OXIDOREDUCTASE
Biological 1. Dehydrogenase : Aerobic
Oxidation Anaerobic
2. Hydroperoxidase : Catalase
Peroxidase
3. Oxidase
4. Oxygenase : Mono-oxygenase
Di-oxygenase
Redox potential of a system is the electron transfer potential E0 or
Redox measure of electron affinity
Complexes are arranged in order of increasing redox potential.
Potential Electron always flow from negative redox potential to positive redox
potential.
Important for transportation of electron.
Complex 1 have more negative redox potential as compared to
complex 4.
Negative redox potential is best donor
Positive redox potential is best acceptor of electrons.
Objective of Respiration :
Energy is released from oxidation reaction in the form of electron.
Electrons are shuttled by electron carriers e.g NAD+ to an ETC.
Electron energy is converted to ATP in the ETC.
Redox Potential
• E0 Volts
• System
• −0.42
• H+/H2 • −0.32
• NAD+/NADH • −0.29
• Lipoate; ox/red • −0.27
• Acetoacetate/3-hydroxybutyrate •
−0.19
• Pyruvate/lactate • −0.17
• Oxaloacetate/malate • +0.03
• Fumarate/succinate • +0.08
• Cytochrome b; Fe3+/Fe2+ • +0.10
• Ubiquinone; ox/red • +0.22
• +0.29
• Cytochrome c1; Fe3+/Fe2+ • +0.82
• Cytochrome a; Fe3+/Fe2+
• Oxygen/water
ATP : Energy
Currency of cell
• Nucleotide
• High energy compound
• Go’= -7.3 kcal/mol
Mitochondria participate in diverse
cellular processes –
Apoptosis
Function of Production of reactive O2 species
Mitochondria
Calcium homeostasis
Immunity
Electron Transport Chain : ETC
• Respiratory chain
• Composed of 5 enzyme complex.
• Complex V belongs to oxidative phosphorylation.
• Location:- Inner Mitochondrial membrane.
• 13 proteins encoded by mitochondrial DNA & nuclear
encoded proteins
Components of ETC
• Complex I :- NADH ubiquinone oxidoreductase
• Complex II :- Succinate ubiquinone oxidoreductase
• Complex III :- Ubiquinone cytochrome c oxidoreductase
• Complex IV :- Cytochrome c oxidase
• Complex V :- ATP synthase complex
Components of ETC
• Sequence of Electron carriers arranged as , metalloenzymes, coenzymes, carrier molecules culminating into
molecular oxygen
1. Dehydrogenase
• NAD-NADH
• FMN-FMNH2 or FAD-FADH2
2.Ubiquinone or Coenzyme Q
3.Iron sulfur protein (FeS) associated With FMN &
• Cytochrome b c c1 ; (Cu containing)
4. Oxidase
• Cytochrome oxidase a, a3
ETC
ETC : Complex I
• NADH Ubiquinone Oxidoreductase
• Integral membrane protein
• Largest complex (Mass 850 kDa), spans both layers of Inner
mitochondrial membrane
• Composed of 45 subunits out of which 7 are of
mitochondrial origin
• Prosthetic groups FMN & Fe-S
•
• Accepts electron from NADH ,produced from
• Pyruvate dehydrogenase complex
• TCA cycle
• Beta oxidation
• Malate aspartate shuttle
•
ETC : Complex II
Succinate - Composed of 4
Peripheral
Ubiquinone subunits which are
membrane protein
Oxidoreductase nuclear DNA origin.
Prosthetic groups Succinate
Mass is 140 kDa.
are FAD & Fe-S. dehydrogenase is-
-Key enzyme of TCA -Only enzyme of TCA inner mitochondrial
cycle cycle located in membrane.
ETC : Ubiquinone Coenzyme
Q10
• Ubiquitous
• Lipophilic
• Mobile carriers
• Not part of ETC
• Not present on inner mitochondrial membrane
•
• Act like electron acceptor or carrier.
• Ubiquinol : Reduced form
• Protects membrane phospholipids and LDL from Lipid peroxidation .
ETC : Complex III
• Ubiquinone cytochrome c oxidoreductase.
• Mass - 250 kDa
• Composed of 11 subunits.
• Only cyto c is encoded by mitochondrial DNA.
• Made of Cyt b, FeS, cyt c1
• Prosthetic groups are heme Non- Heme Iron ( NHI) & Fe-S
• Cyt c is,
• Water soluble
• Easily diffusible
• Plays important role in programmed cell death.
•
ETC : Complex IV :
Oxidase
• Cytochrome C oxidase : Cyt a-a3
• Contains cyt a,& cyt a3.
• Composed of 13 subunits
• 3 of them are mitochondrial origin
• Utilises molecular oxygen to accept electron donated
by cyt. C
• Contains Copper at its center.
• Oxygen is the final electron acceptor of ETC.
• 4 electrons fron Cyt c required for complete
• reduction of molecular oxygen to “Water “
Complex V ??? : ATP
synthase
• During the transfer of electron through ETC energy is
produced.
• This energy is coupled to the formation of ATP molecules
by phosphorylation of ADP by
• Fo F1 ATPase synthase complex.
• Phosphorylation of ADP into ATP is coupled with
oxidation of reducing equivalents, thus oxidative
phosphorylation.
• Fo subunit : ion channel, provides for a proton flux back
into mitochondrial matrix .
Flow of electrons in ETC
• Dr. N. Guha Niyogi
• Asstt Professor, Biochemistry, GGMC
Biological • Ist MBBS Biochemistry
• 31/10/22
Oxidation
• THANK YOU
