BIOC 212 Lecture Notes - Lecture 55: Beta Oxidation, Lipid Bilayer, Succinate Dehydrogenase
29 May 2018
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Metabolism XVII
Iron Atoms Cooperate to Bind Electrons
• Cysteine side chains & free sulfur atoms coordinate 2-4 iron ions (Fe3+)
o C side chains & free S atoms form a cubes in space with iron atoms
o Called a coordinated bond
• Non-covalent ways of binding metal ions
• Share electrons but not completely
• Iron ions do not have access to electrons from sulfur, but the electrons from S
hold them in space
o There are 2-3 different conformations of iron-sulfur clusters
o Geometry of how it is held in the protein determines its exact redox potential
• In a 2 iron Fe-S cluster, can share an electron between two different ions
o From a quantum mechanics stand point, the electron can jump between two
irons and distribute the charge across the two ions
o Relatively stable electron binders that do not need to form a covalent bond
with another ion when bound to electrons
• Electron binding reduces one Fe3+ to Fe2+
o But is stabilized by other Fe3+ ions
• Precise geometry of the atoms determine reduction potential of cluster
Complex I
• In complex I, the proton pumps are in the membrane
o Pass H+ through a channel that is embedded in the membrane
o But electrons themselves actually move through a different arm of the
protein
o All inside the mt matrix, where all NADH being generated from citric acid
cycle
• Electrons start off on the matrix side, and travel through the protein down to the
interface down to the interface with the IM
o At the interface, complex I hands electrons from Fe-S core off to another
covalent carrier
o Special molecule called ubiquinone, or coenzyme Q
Ubiquinone Carries Electrons Inside the Membrane
• Ubiquinone or coenzyme Q is a membrane-soluble carrier molecule for electrons
o Similar in how binds electrons to NADH and FAD
o Covalent carrier
o Binds protons as it binds electrons
