Krebs cycle Flashcards
Citric Acid Cycle synonyms
Tricarboxylic Acid cycle (TCA cycle)
Krebs Cycle
Citric Acid cycle
Acetyl CoA-> CO2
Citrate Synthase
- Reaction Type
- Int
- regulation
Acetyl CoA + Oxaloacetate -> Citrate Reaction type: -aldol condensation followed by hydrolysis that releases CoA into solution -intermediate= Citryl CoA -REGULATED
Citrate Synthase enzyme Structure
Dimer with sequential ordered kinetics
a) oxaloacetate binds (2 binding sites)
2) Acetyl-CoA binds
Minimizes site reacting by ordered binding
Aconitase
- Reaction type
- Int
- Regulation
Citrate-> Isocitrate
Reaction type:
Isomerization
-dehydration followed by hydration reaction
Intermediate-Cis-Aconitate
Regulation
Structure of Aconitase
Iron Sulfur protein or Nonheme-iron protein
4 iron atoms (Fe) complex to:
- 3 cysteine residues sulfurs
- 4 inorganic sulfides
1 Fe binds citrate by carboxyl (COO-) and Hydroxyl (OH-)
Isocitrate Dehydrogenase
- Reaction type
- Int
- Regulation
Isocitrate-> Alpha ketogluterate
Reaction type:
Oxidative Decarboxylation
-NADH produced (before Intermediate)
-CO2 Produced (after Intermediate)
Intermediate:
Oxalosuccinate
Regulated-YES
Alpha Ketogluterate Dehydrogenase
- Reaction type
- Int
- Regulation
Alph Ketogluterate-> Succinyl CoA
Reaction Type:
Oxidative decarboxylation
-NADH and CO2 produced
No Intermediate
Regulation-YES
Similar to Pyruvate dehydrogenase complex
- 3 enzyme compllex
- same prosthetic groups and cofactors
- E3 exactly the same
Succinyl CoA Synthetase
- Reaction type
- Int
- Regulation
(AKA succinate thiokinase)
Succinyl CoA-> Succinate + CoA + GTP
Reaction type
- Transfer from
- substrate level phosphorylation-GTP produced
- *use of GDP or ADP (or other nucleotide diphosphate) is species dependent and Nucleotide diphosphokinase can interconvert various NTPs
- Thioster is High Energy Bond
Succinyl CoA Synthetase Mechanism
1) Displacement of coenzyme A by orthophosphate which generates an energy rich compound succinylcholine phosphate
2) His residue plays a key role as a moving arm that detaches the phosphoryl group to form ATP and forms succinate which leaves the reaction
Succinyl CoA Structure
A2B2 heterodimer
- A subunit contains Rossmann Fold that binds ADP substrates of succinylcholine CoA synthetase
- B subunit contains ATP binding “grasp” domain-binds ADP and activates it
Succinate Dehydrogenase
- Reaction type
- Int
- Regulation
Succinate-> Fumurate Reaction type: Oxidation/reduction reaction -FAD reduced to FADH2, FAD is the hydrogen acceptor because the free energy change is insufficient to reduce NAD+ -Succinate oxidized to Fumurate
Intermediate-NO
Regulation-NO
**Directly associated with the electron transporting chain by transferring 2 electrons to CoQ
Succinate Dehydrogenase Structure
Membrane bound Heterodimer with 3 types of iron-sulfur complexes:
- 2Fe-2S (2 irons bound to two inorganic sulfides)
- 3Fe-4S (3 irons bound to 4 inorganic sulfides)
- 4Fe-4S ( 4 irons bound to 4 inorganic sulfides)
Fumurase
- Reaction type
- Int
- Regulation
AKA fumigate hydratase
Fumurate-> L-Malate
Reaction type:
Hydration
-reversible reaction
No regulation or Intermediate
Where is Malate also produced in?
- Urea cycle
- Purine Synthesis
- Catabolism of Phe and Tyr
- Gluconeogenesis- OAA to PEP
Malate Dehydrogenase
- Reaction type
- Int
- Regulation
Malate-> Oxaloacetate
Reaction Type:
Oxidation/Reduction
-NAD+ reduced to NADH
-Malate oxidized to Oxaloacetate
