Metabolism and Metabolic Disease

BI520 Metabolism and Metabolic Disease

Mitochondrial Electron Transport

Mitochondrial ATP Synthesis

ATP yield and Mitochondrial Metabolic Disease

Inhibitors and Uncouplers of Electron Transport and Oxidative Phosphorylation



Inherited Metabolic Disease Processes

Metabolism of Amino Acids and Nucleotides

Urea Cycle (Ornithine Cycle)

Cholesterol Metabolism

Vitamins and Malnutrition

Haem and Disease

Tetrapyrroles

Tetrapyrroles II



Glucose Transporters: Diversity and Mechanisms

Insulin Mechanisms

Diabetes Mechanisms

Diabetes Mechanisms II

Glycogen and Glycogen Storage Diseases

Treatments for Type 2 Diabetes

,Mitochondrial Electron Transport

Protein carriers
- Ubiquinones
o Uses benzoquinone (Q – QH – QH2).
- Cytochromes
o Use haem prosthetic groups with Fe2+.
- Copper complexes
o Copper ions complexed to cysteine or haem.

- The transfer of electrons from NADH to O2 yields (ΔGo’) -52.5 kcal/mol.
o Each pair of electrons that reduce O2 to H2O.

Iron-sulphur proteins
- FeS proteins
o These are proteins containing one or more FeS clusters. These clusters
take part in redox reactions and so are a part of the ETC. FeS clusters
have roles in catalysis and the sensing of ambient conditions
(temperature, humidity and air pressure). E.g. aconitase.
- Cofactors
o The Fe2+ ion can form 6 coordinate bonds, 4 of which is to the nitrogen
atom of the tetrapyrrole ring. The 5th is to the histidine of the globin
molecule, known as the proximal histidine. The 6th is empty, awaiting the
O2 molecule.
o O2 release is so exceptional in Hb because of a distal histidine molecule.
It hovers close to the O2-binding site and prevents O2 forming a linear
bond with Fe.
o Instead of Fe2+ oxidising to Fe3+, a complex of Fe2+-O2 is formed, which
is more desirable. This is because Fe3+ binds O2 very poorly and so the
FeO2 complex favours easy release due to it being bent at 120o. this
results in weaker O2 binding. To summarise, distal histidine prevents
neighbouring Hb from oxidising Fe (II) to Fe (III).
o Distal histidine also prevents CO from binding irreversibly to the Fe atom.
o This is done in the same way preventing oxidation of Fe2+ to Fe3+. The
presence of the distal histidine prevents the linear CO bond and so the
angled bond interaction reduces CO’s affinity for Fe2+ somewhat.
o Distal histidine also stabilises the oxygen binding to Fe by hydrogen
bonding to the oxygen molecule.

, Cytochrome cofactors
- 3 types: a, b, c (differs by absorption wavelength).
- Intracellular haem proteins that undergo redox reactions. Upon reduction they
show strong absorption at ~510nm.
- The structure of the different cytochromes gives rise to different redox
properties.




Complex I (NADH Dehydrogenase)
- Transfer of hydride ions from NADH to FMN.
- 2e- - FeS – N-2 (FeS protein) – ubiquinone (QH2).
- 4H+ ions pumped into the intermembrane space.

Complex II
- Electrons – FAD – FeS – CoQ.
- Electrons also obtained through the glycerol-phosphate shuttle by G3PD.
- Acyl CoA Dehydrogenase
o Catalyses the first step of β-oxidation. It has an FAD cofactor which
transfers electrons to the ETC.

Complex III (cyt. bc1)
- Bifurcation is the division of processes into two branches or pathways.
- Subunits: Rieske FeS proteins, cyt. c1, cyt. b.
- Antimycin A
o Interferes with electron transfer from cyt. bH to ubiquinone so it’s reduced
and not oxidised.
- Myxothiazol
o Prevents electron flow from ubiquinol to Rieske FeS by binding to
ubiquinone.

Q cycle
- FeS centre is known as the Rieske protein.
- Vectoral translocation
o The Q cycle involves vectoral translocation of protons instead of proton
pumping. This is where protons are consumed at the matrix side (QH2)
and released into the IMS by diffusion.
- Cycle I
o The Q cycle is the transfer of electrons from QH2 to cyt. c. QH2 can
transport 2e-, whereas cyt. c can only carry 1e-. Overall, QH2 is oxidised
to Q and 2 cyt. c is reduced. Cyt. c is soluble and so can diffuse across
the IMS to complex IV. The electron it carries is bound to a single haem
group.