CHEM 3050 Lecture Notes - Lecture 8: Citric Acid Cycle, Oxidative Phosphorylation, Malic Acid
2 May 2018
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CHEM 3050
Lecture 8
Enzyme has phosphorylated intermediate that is bound to the
enzyme (uses His in the mechanism)
A phosphohistidine intermediate transfers the phosphate to GDP
Step 6: Oxidation of Succinate to Fumarate… via succinate
dehydrogenase
middle point of the cycle; all the oxidative carboxylation has taken
place, must build the carbon skeleton back up to the top of the
cycle so it can go again it just went through a lot of exergonic
processes and released a lot of its energy, so now it needs to go
back up to the top and start all over again run in reverse of
oxidative phosphorylation; FAD is covalently linked to the enzyme
∆G’⁰= 0kJ/mol equilibrium, can go both ways
FAD linked because it needs strong oxidant
Step 7: Hydration of Fumarate to Malate… via Fumarase
Fumarate is a trans alkene and malate is all single bonds
makes it incredibly stereospecific in the forward and reverse
direction
find more resources at oneclass.com
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Document Summary
Enzyme has phosphorylated intermediate that is bound to the enzyme (uses his in the mechanism) A phosphohistidine intermediate transfers the phosphate to gdp. G" = 0kj/mol equilibrium, can go both ways. Step 7: hydration of fumarate to malate via fumarase. Fumarate is a trans alkene and malate is all single bonds makes it incredibly stereospecific in the forward and reverse direction. Needs trans c==c fumarate and selective for l-malate over d- malate. Step 8: oxidation of malate to oxaloacetate via malate. Under standard conditions, this reaction is highly endergonic. Exact mechanism is unknown, but it must involve hydride transfer to nad+ to make nadh in a similar way to other dehydrogenases. Low retention time of any of the intermediates with a near zero. The front end is so exergonic (highly negative g), you"re driving it to come back by near neutral reactions as the cycle goes around.
