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Flashcards in Enzymes Deck (72):
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

31

Alpha-Ketoglutarate Dehydrogenase
- TCA Cycle (highly regulated)
- Cofactors: B1, B2, B3, B5, lipoic acid

Alpha-KG (5C) --> CO2 + NADH + succinyl CoA (4C)
- Inhibited by: ATP, NADH, succinyl CoA
- Requires same cofactors as pyruvate dehydrogenase complex (B1, B2, B3, B5, lipoic acid)

32

Complex 1
- ETC (oxidative phosphorylation)

- NADH --> NAD+ --> 2.5 ATP
- Inhibited by Amytal (barbiturate), Rotenone (pesticide/fish poison), MPP (also causes Parkinson's)

33

Complex II (Succinate Dehydrogenase)
- ETC (oxidative phosphorylation)

FADH2 --> FAD --> 1.5 ATP

34

Complex III
- ETC (oxidative phosphorylation)

Inhibited by Antimycin A (fish poison)

35

Complex IV
- ETC (oxidative phosphorylation)

1/2 O2 + 2H+ --> H2O
- Inhibited by CN, sodium azide, CO, H2S

36

Complex V (ATPase)
- ETC (oxidative phosphorylation)

- Generates ATP
- Inhibited by Oligomycin (macrolide ABx)

37

Alanine Aminotransferase
- Transamination
- Cofactor: pyridoxal phosphate (B6)

Alanine + alpha-KG --> pyruvate + glutamate
- Marker for hepatocyte damage

38

Aspartate Transaminase
- Transamination
- Cofactor: pyridoxal phosphate (B6)

Aspartate + alpha-KG --> oxaloacetate + glutamate
- Marker for hepatocyte damage

39

G6P Dehydrogenase
- HMP Shunt (pentose phosphate pathway) [rate limiting step]

G6P + NADP+ --> 2 NADPH + Ribulose-5-P + CO2
- NADPH --> glutathione reduction inside RBCs, FA and cholesterol biosynthesis
- Ribulose-5-P --> PRPP --> nucleotide synthesis (ribose backbones)
- Inhibited by NADPH
- Deficiency --> hemolytic anemia

40

NADPH Oxidase
- Respiratory Burst
- Requires NADPH

O2 --> superoxide ion
- In phagolysosome
- Deficiency: chronic granulomatous disease

41

Superoxide Dismutase
- Respiratory burst

Superoxide ion --> hydrogen peroxide
- In phagolysosome

42

Myeloperoxidase
- Respiratory burst

Hydrogen peroxide + Cl- --> hypochlorous acid (bleach)
- In phagolysosome

43

Glutathione Peroxidase
- RBC Detox

H2O2 + reduced glutathione (important antioxidant) --> H2O + glutathione disulfide (oxidized)

44

Glutathione Reductase
- Uses NADPH (from G6PD)

NADPH + glutathione disulfide (oxidized) --> NADP+ + reduced glutathione

45

Fructokinase
- Fructose metabolism
- Requires ATP

Fructose + ATP --> F1P
- Defect: essential fructosuria (benign)

46

Aldolase B
- Fructose metabolism

F1P --> dihydroxyacetone P and glyceraldehyde
- Defect: fructose intolerance (inhibits glycogenolysis and gluconeogenesis --> fasting hypoglycemia)

47

Galactokinase
- Galactose metabolism
- Requires ATP

Galactose + ATP --> Galactose-1-P
- Defect: galactokinase deficiency (infantile cataracts)

48

Aldose Reductase
- Galactose metabolism

Galactose --> galactitol
- too much galactitol --> cataracts

49

Galactose-1-Phosphate Uridyltransferase
- Galactose metabolism

Galactose-1-P + UDP-Glucose --> Glucose-1-P + UDP-Galactose --> glycolysis/glycogenolysis
- Defect: classic galactosemia

50

HMG-CoA Synthase
- Ketogenesis (rate-limiting)

Makes ketone bodies during starvation

51

Alcohol Dehydrogenase
- Ethanol metabolism
- NAD+ is limiting reagent

Ethanol + NAD+ --> Acetaldehyde + NADH
- 0-order kinetics
- Acetaldehyde is what causes hangover
- Inhibited by Fomepizole (used for methanol or ethylene glycol poisoning)

52

Acetaldehyde Dehydrogenase
- Ethanol metabolism
- NAD+ is limiting reagent

Acetaldehyde + NAD+ --> Acetate + NADH
- Inhibited by disulfiram (acetaldehyde accumulates --> hangover sx)

53

ApoE
- Lipid transport

Mediates remnant uptake

54

Apo A-1
- Lipid transport

Activates LCAT --> catalyzes esterification of cholesterol
- Nascent HDL --> mature HDL

55

Apo C-II
- Lipid transport

Lipoprotein lipase cofactor
- Deficient in Type I (Hyperchylomicronemia)

56

Apo B-48
- Lipid transport

Mediates chylomicron secretion

57

Apo B-100
- Lipid transport

Mediates VLDL secretion
- Binds LDL R
- Defective binding in Type IIa (familial hypercholesterolemia)

58

HMG-CoA Reductase
- Cholesterol synthesis (rate limiting step)

Converts HMG-CoA to mevalonate
- Induced by insulin
- Inhibited by statins
- Cholesterol synthesis starts with acetyl CoA

59

Acetyl CoA Carboxylase
- FA Synthesis (rate limiting step)

- Cytoplasm of hepatocytes

60

Carnitine Acyltransferase 1 (Caritine Palmitoyltransferase 1)
- FA Degradation (rate limiting step)

- Mitochondrial matrix

61

Phenylalanine Hydroxylase
- Catecholamine synthesis/tyrosine catabolism
- Cofactor: BH4

Phenylalanine --> Tyrosine
- Tyrosine used to make thyroxine
- Deficient: PKU

62

Tyrosine Hydroxylase
- Catecholamine synthesis/ tyrosine catabolism
- Cofactor: BH4

Tyrosine --> Dopa
- Dopa used to make melanin

63

Dopa Decarboxylase
- Catecholamine synthesis/tyrosine catabolism
- Cofactor: B6

DOPA --> Dopamine
- Inhibited by Carbidopa (rx for Parkinson's)

64

Dopa-beta-hydroxylase
- Catecholamine synthesis/tyrosine catabolism
- Cofactor: Vit C

Dopamine --> NE
Deficiency: nasal congestion, ptosis, orthostatic hypotension

65

Phenylethanolamine-N-methyltransferase
- Catecholamine synthesis/tyrosine catabolism
- Cofactor: SAM (transfers methyl groups)

NE --> Epi
- Stimulated by cortisol

66

Carbamoyl Phosphate Synthetase I
- Urea cycle (rate-limiting step)
- Requires ATP

CO2 + NH3 --> Carbamoyl phosphate
- In mitochondria

67

Ornithine Transcarbamylase
- Urea cycle

Carbamoyl phosphate + ornithine --> citrulline

68

Tyrosinase
- Catecholamine synthesis/tyrosine catabolism

Dopa --> melanin
- Deficiency: albinism

69

Homogentisate Oxidase
- Catecholamine synthesis/tyrosine catabolism

Homogentisic acid (from Tyr) --> maleylacetoacetic acid --> fumarate --> TCA cycle
- Deficiency: alkaptonuria (ochronosis, black urine)

70

Cystathione Synthase
- Homocysteine metabolism
- Cofactor: B6

Serine + homocysteine --> cystathione
Deficiency: homocystinuria

71

Methionine Synthase
- Homocysteine metabolism
- Cofactor: B12

Homosysteine --> methionine
Deficiency: homocystinuria

72

Alpha-ketoacid Dehydrogenase
- AA metabolism
- Cofactors: thiamine pyrophosphate, lipoate, coenzyme A, FAD, NAD

Degrades branched AA (isoleucine, leucine, valine)
Deficiency: maple syrup urine disease