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Lecture 21 Pyruvate Dehydrogenase Complex-BW

Bond cant c atalyze the reverse r eaction mcb 2000

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Unformatted text preview: r eaction. MCB 2000 Lecture 21 Mechanism of Pyruvate Dehydrogenase Complex Step 1: Decarboxylation of pyruvate (involves E1-pyruvate dehydrogenase component) 4/6/13 Loss hydrogen and get a neg charge - carbanion form will attack pyruvate - the CO2 will be eliminated - add two hydrogen across caboxyl group - the ionic form - elmination of CO2 and the attachment of something. MCB 2000 Lecture 21 Reaction catalyze by E1 and now it actually has two carbon bound to it. and ionized next step invovles the interaction between E1 and E2. where E2 has a long arm - the side cahin of lysine is long side chain - attach and E2 arm swings over to E1 and it will attach the two carbons. the disulfi de bonds - become reduced. the two carbons are now transfer to E1 reduced on disulfi de bond and forming biester bond. Mechanism of Pyruvate Dehydrogenase Complex E2 Step 2: Oxidation & transfer Acetyl group formed and transferred to lipoamide. Once two carbons trasnfer the important c bond form between the two carbons - is thioester bond keep in mind - that you have enzyme complex substrate or intermediate products are not going to diffuse away until the r action is fi nished. - effi ceiney of reaction. two c arbons can easily diffuse away but they wont because they are bound to the coenzyme. Results in formation of thioester bond (high energy) Catalyzed by E1--pyruvate dehydrogenase component Bound to E2--Transacetylase 4/6/13 the reaction itself the lipamide arm as swung over to E1 and picked up two carbons. and now reduced. MCB 2000 Lecture 21 Mechanism of Pyruvate Dehydrogenase Complex Step 3: Formation of Acetyl CoA Transfer of acetyl group to CoA Catalyzed by E2--Transacetylase Thioester bond Now CoA is entering the complex - acetlyl Coa need to leave the complex to enter the TCA cycle cant exit with it being bound to something. next reaction E2 - transfer the two carbons onto CoA - prduce still going to conserve the thisoster bond - accept carbons and maintin thioester bonds - acetyl CoA can now elave the complex whenever you want. getting back disulfi de bond . 4/6/13 MCB 2000 Lecture 21 Mechanism of Pyruvate Dehydrogenase Complex Step 4: Oxidation of Dihydrolipoamide Allows for another catalytic cycle (reset PDC) Catalyzed by E3 Dihydrolipoyl dehydrogenase Transfer of electrons from FADH2 to NAD+ FAD is a prosthetic group on E3 4/6/13 Transfer the elctrons - capture some electrons add hydrogens - transfered to FAD. got disulfi de bond back FAD now has protons and elctrons - also FAD is bound to the complex. as a result it needs to transfer the hydrogens and elctrons to NAD+ and then it can then leave the c omplex. FADH2 hands over elctrons to NAD+ and now r egenreated - got back FAD from the reduced form - back to square 1 MCB 2000 Lecture 21 FAD Summary of PDC Reaction Oxidative decarboxylation Generates a high energy thioester bond (Acetyl CoA) Produces NADH (will donate electrons to ETC) Produces CO2 even though reducing is not part of the respirction -...
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