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Flashcards in Enzymes Deck (72)
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1

Carbamoyl Phosphate Synthetase II
- Pyrimidine Synthesis (rate-limiting)

Glutamine + CO2 + 2ATP --> Carbamoyl phosphate
- Cytosol
- N from glutamine

2

UMP Synthase
- Pyrimidine Synthesis

Orotic acid + PRPP --> UMP
- Impaired in orotic aciduria

3

Ribonucleotide Reductase
- Pyrimidine Synthesis

UDP --> dUDP
- Inhibited by hydroxyurea (sickle cell, cancer)

4

Thymidylate Synthase
- Pyrimidine Synthesis

dUMP --> dTMP
- uses THF (have to have folic acid to synthesize DNA)
- Inhibited by 5-FU (cancer)

5

Dihydrofolate Reductase
- Pyrimidine Synthesis

Regenerates THF from DHF after it's used by thimidylate synthase
- Inhibited by methotrexate (eukaryotes), trimethoprim (prokaryotes), and pyrimethamine (protozoa)

6

Glutamine PRPP Amidotransferase
- Purine Synthesis (rate-limiting)

PRPP --> IMP
- Inhibited by 6-MP (cancer)

7

IMP Dehydrogenase
- Purine Synthesis

IMP --> GMP
- Inhibited by mycophenolate

8

Xanthine Oxidase
- Purine Salvage

Hypoxanthine --> xanthine
Xanthine --> uric acid
- Inhibited by allopurinol and febuxostate (gout)
- Metabolizes azathioprine and 6-MP (increases toxicity)

9

HGPRT
- Purine Salvage

Hypoxanthine --> IMP
Guanine --> GMP
- Deficient in Lesch Nyhan Syndrome

10

Adenosine Deaminase
- Purine salvage

Adenosine --> Inosine
- Deficiency causes SCID

11

Glucokinase
- Glycolysis (first committed step)
- Glycogen synthesis

Glucose --> glucose-6-phosphate
- Found in liver, beta cells of pancreas
- High Km (needs a lot of glucose)
- High Vmax (works quickly)
- Induced by insulin
- Mutation --> maturity onset diabetes of the young

12

Hexokinase
- Glycolysis (first commited step)
- Glycogen synthesis

Glucose--> glucose-6-phosphate
- Most tissues
- Low Km (higher affinity)
- Low Vmax (low capacity)
- Not induced by insulin

13

Phosphofructokinase-1
- Glycolysis (rate-limiting step)
- Requires ATP

F-6-P --> F-1,6-BP
- Stimulated by: AMP (not a lot of ATP around), F-2,6-BP
- Inhibited by: ATP (high energy state), citrate (substrate of TCA cycle)

14

Pyruvate Kinase
- Glycolysis
- Produces ATP

Phosphoenolpyruvate --> pyruvate --> TCA cycle
Stimulated by: F-1,6-BP (upstream substrate)
Inhibited by: ATP, alanine (high energy state)

15

Phosphofructokinase-2
- Glycolysis (regulating step)

F-6-P --> F-2,6-BP --> allosteric activator of PFK-1 (glycolysis substrate)
Stimulated by: insulin (fed state)

16

Fructose-bisphosphatase-2
- Glycolysis (regulating step)

F-2,6-BP --> F6P --> gluconeogenesis
Stimulated by: glucagon (fasting)

17

Pyruvate Carboxylase
- Gluconeogenesis
- Requires biotin

Pyruvate --> oxaloacetate
- Requires biotin
- Stimulated by: acetyl Co-A

18

PEP Carboxykinase
- Gluconeogenesis

Oxaloacetate --> PEP

19

Fructose-1,6-Bisphosphatase
- Gluconeogenesis (rate-limiting)

F-1,6-BP --> F6P
- Stimulated by: ATP (high energy)
- Inhibited by: AMP, F-2,6-BP (energy deficient)

20

Glucose-6-Phosphatase
- Gluconeogenesis (last step)
- Glycogenolysis (last step)

G6P --> glucose
- deficient in Von Gierke Disease
- NOT in muscles (can't do gluconeogenesis) - only reason muscle cells break down glycogen is for its own use (doesn't share energy)

21

Glycogen Synthase
- Glycogen synthesis (rate-limiting)

UDP-Glucose --> Glycogen
- Makes alpha-1,4-glycosidic linkages
- Stimulated by insulin

22

Glycogen Phosphorylase
- Glycogenolysis

Liberates G1P residues off branched glycogen until 4 glucose units remain on a branch
- Breaks alpha-1,4 linkage
- Inhibited by: ATP, G6P, glucose, insulin
- Stimulated by: glucagon (by activating GP kinase), Epi (Gs)
- Deficient in McArdle Disease (Type V)

23

Phosphoglucomutase
- Glycogenolysis

G1P --> G6P

24

Debranching Enzyme
- Glycogenolysis

4-alpha-D-glucanotransferase: removes 3 molecules of G1P from branch to linkage
alpha-1,6-glucosidase: cleaves off last residue --> liberates glucose
- Deficient in Cori Diseaes (Type III)

25

Pyruvate Carboxylase
- Pyruvate Metabolism
- Requires biotin

Pyruvate + ATP + CO2 --> oxaloacetate --> TCA cycle or gluconeogenesis
- Cofactor: biotin

26

Pyruvate Dehydrogenase
- Pyruvate Metabolism
- Requires B1, B2, B3, B5, lipoic acid

Pyruvate + NAD+ + CoA --> AcetylCoA + CO2 + NADH
- Transition from glycolysis to TCA cycle
- Cofactors: TPP (B1), lipoic acid (inhibited by arsenic - garlic breath), Coenzyme A (B5), FAD (B2), NAD+ (B3)
- Activated by: increased NAD+/NADH ratio, high ADP, high Ca2+

27

Lactic Acid Dehydrogenase
- Pyruvate Metabolism
- Requires B3

Pyruvate --> lactate (requires NADH) --> Cori Cycle
- End of anaerobic glycolysis (major pathway in RBCs, WBCs, kidney medulla, lens, testes, and cornea)
- For cells that like mitochondria
- Deficiency leads to exercise intolerance

28

Alanine Aminotransferase
- Pyruvate Metabolism
- Requires B6

Pyruvate --> Alanine --> Cahill Cycle
- Alanine carries amino groups to the liver from muscle

29

Citrate Synthase
- TCA Cycle

Acetyl-CoA (2C) + oxaloacetate (4C) --> Citrate (6C)
- Inhibited by ATP

30

Isocitrate Dehydrogenase
-TCA Cycle

Isocitrate (6C) --> CO2 + NADH + alpha-ketoglutarate (5C)
- Inhibited by: ATP, NADH
- Stimulated by: ADP