Lecture+18+Citric+acid+cycle notes

Citrate has no chiral carbons symmetry of this

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Unformatted text preview: ld not be correct! •Citrate has no chiral carbons. "Symmetry" of this compound should scramble the label? citrate is symmetrical so it seemed that the coo- groups should be indistringuashable so why wasn't the label scrambled? 6 it has a subtle type of asymmetry 5 Citrate has a previously unrecognized type of asymmetry - it has a prochiral carbon. know xray crystal structure take citrate dehydrate it put hydroxyl group on the 2 position as long as the enzyme contacts 3 substituates coming off the central carbon the enzyme can distinguish the 2 ch2coo- groups this type of asymmetriy is prochiral prosthetic group involved in oxidation/red ≥3 contacts w/ enzyme Mechanism: remove H20, flip bound substrate 180°, stereospecifically add back H20. 7 8 flip rehydrate Mammalian pyruvate dehydrogenase (cutaway veiw of dodecahedral structure) Pyruvate dehydrogenase pyruvate + NAD+ + CoA acetyl CoA + CO2 + NADH Three polypeptides: E1, E2, E3 Purified enzyme is a huge protein complex ~500 Å across. Core of 60 E2 (20 trimers) 12 E3 and 60 E1 are bound to the core ~100X bigger than a typical enzyme complex of a bunch of proteins can see with elecronn micrograph super big normal techniques don't work for such big enzymes using electon microscopy with low resolution images but when you get thousands of these images you can good info cryoEM not atomic resolution but pretty close blue thing is part of E2 complex has 5 rxns that add to net total E2 has a swinging arm (blue...
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