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Enzymes Flashcards

1
Q

Carbamoyl Phosphate Synthetase II

- Pyrimidine Synthesis (rate-limiting)

A

Glutamine + CO2 + 2ATP –> Carbamoyl phosphate

  • Cytosol
  • N from glutamine
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2
Q

UMP Synthase

- Pyrimidine Synthesis

A

Orotic acid + PRPP –> UMP

- Impaired in orotic aciduria

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3
Q

Ribonucleotide Reductase

- Pyrimidine Synthesis

A

UDP –> dUDP

- Inhibited by hydroxyurea (sickle cell, cancer)

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4
Q

Thymidylate Synthase

- Pyrimidine Synthesis

A

dUMP –> dTMP

  • uses THF (have to have folic acid to synthesize DNA)
  • Inhibited by 5-FU (cancer)
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5
Q

Dihydrofolate Reductase

- Pyrimidine Synthesis

A

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

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6
Q

Glutamine PRPP Amidotransferase

- Purine Synthesis (rate-limiting)

A

PRPP –> IMP

- Inhibited by 6-MP (cancer)

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7
Q

IMP Dehydrogenase

- Purine Synthesis

A

IMP –> GMP

- Inhibited by mycophenolate

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8
Q

Xanthine Oxidase

- Purine Salvage

A

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

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9
Q

HGPRT

- Purine Salvage

A

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

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10
Q

Adenosine Deaminase

- Purine salvage

A

Adenosine –> Inosine

- Deficiency causes SCID

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11
Q

Glucokinase

  • Glycolysis (first committed step)
  • Glycogen synthesis
A

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
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12
Q

Hexokinase

  • Glycolysis (first commited step)
  • Glycogen synthesis
A

Glucose–> glucose-6-phosphate

  • Most tissues
  • Low Km (higher affinity)
  • Low Vmax (low capacity)
  • Not induced by insulin
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13
Q

Phosphofructokinase-1

  • Glycolysis (rate-limiting step)
  • Requires ATP
A

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)
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14
Q

Pyruvate Kinase

  • Glycolysis
  • Produces ATP
A

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

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15
Q

Phosphofructokinase-2

- Glycolysis (regulating step)

A

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

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16
Q

Fructose-bisphosphatase-2

- Glycolysis (regulating step)

A

F-2,6-BP –> F6P –> gluconeogenesis

Stimulated by: glucagon (fasting)

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17
Q

Pyruvate Carboxylase

  • Gluconeogenesis
  • Requires biotin
A

Pyruvate –> oxaloacetate

  • Requires biotin
  • Stimulated by: acetyl Co-A
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18
Q

PEP Carboxykinase

- Gluconeogenesis

A

Oxaloacetate –> PEP

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19
Q

Fructose-1,6-Bisphosphatase

- Gluconeogenesis (rate-limiting)

A

F-1,6-BP –> F6P

  • Stimulated by: ATP (high energy)
  • Inhibited by: AMP, F-2,6-BP (energy deficient)
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20
Q

Glucose-6-Phosphatase

  • Gluconeogenesis (last step)
  • Glycogenolysis (last step)
A

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)
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21
Q

Glycogen Synthase

- Glycogen synthesis (rate-limiting)

A

UDP-Glucose –> Glycogen

  • Makes alpha-1,4-glycosidic linkages
  • Stimulated by insulin
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22
Q

Glycogen Phosphorylase

- Glycogenolysis

A

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)
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23
Q

Phosphoglucomutase

- Glycogenolysis

A

G1P –> G6P

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24
Q

Debranching Enzyme

- Glycogenolysis

A

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)

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25
Q

Pyruvate Carboxylase

  • Pyruvate Metabolism
  • Requires biotin
A

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

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26
Q

Pyruvate Dehydrogenase

  • Pyruvate Metabolism
  • Requires B1, B2, B3, B5, lipoic acid
A

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+
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27
Q

Lactic Acid Dehydrogenase

  • Pyruvate Metabolism
  • Requires B3
A

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
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28
Q

Alanine Aminotransferase

  • Pyruvate Metabolism
  • Requires B6
A

Pyruvate –> Alanine –> Cahill Cycle

- Alanine carries amino groups to the liver from muscle

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29
Q

Citrate Synthase

- TCA Cycle

A

Acetyl-CoA (2C) + oxaloacetate (4C) –> Citrate (6C)

- Inhibited by ATP

30
Q

Isocitrate Dehydrogenase

-TCA Cycle

A

Isocitrate (6C) –> CO2 + NADH + alpha-ketoglutarate (5C)

  • Inhibited by: ATP, NADH
  • Stimulated by: ADP
31
Q

Alpha-Ketoglutarate Dehydrogenase

  • TCA Cycle (highly regulated)
  • Cofactors: B1, B2, B3, B5, lipoic acid
A

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
Q

Complex 1

- ETC (oxidative phosphorylation)

A
  • NADH –> NAD+ –> 2.5 ATP

- Inhibited by Amytal (barbiturate), Rotenone (pesticide/fish poison), MPP (also causes Parkinson’s)

33
Q 
Complex II (Succinate Dehydrogenase)
- ETC (oxidative phosphorylation)
A

FADH2 –> FAD –> 1.5 ATP

34
Q

Complex III

- ETC (oxidative phosphorylation)

A

Inhibited by Antimycin A (fish poison)

35
Q

Complex IV

- ETC (oxidative phosphorylation)

A

1/2 O2 + 2H+ –> H2O

- Inhibited by CN, sodium azide, CO, H2S

36
Q 
Complex V (ATPase)
- ETC (oxidative phosphorylation)
A
  • Generates ATP

- Inhibited by Oligomycin (macrolide ABx)

37
Q

Alanine Aminotransferase

  • Transamination
  • Cofactor: pyridoxal phosphate (B6)
A

Alanine + alpha-KG –> pyruvate + glutamate

- Marker for hepatocyte damage

38
Q

Aspartate Transaminase

  • Transamination
  • Cofactor: pyridoxal phosphate (B6)
A

Aspartate + alpha-KG –> oxaloacetate + glutamate

- Marker for hepatocyte damage

39
Q

G6P Dehydrogenase

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

A

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
Q

NADPH Oxidase

  • Respiratory Burst
  • Requires NADPH
A

O2 –> superoxide ion

  • In phagolysosome
  • Deficiency: chronic granulomatous disease
41
Q

Superoxide Dismutase

- Respiratory burst

A

Superoxide ion –> hydrogen peroxide

- In phagolysosome

42
Q

Myeloperoxidase

- Respiratory burst

A

Hydrogen peroxide + Cl- –> hypochlorous acid (bleach)

- In phagolysosome

43
Q

Glutathione Peroxidase

- RBC Detox

A

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

44
Q

Glutathione Reductase

- Uses NADPH (from G6PD)

A

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

45
Q

Fructokinase

  • Fructose metabolism
  • Requires ATP
A

Fructose + ATP –> F1P

- Defect: essential fructosuria (benign)

46
Q

Aldolase B

- Fructose metabolism

A

F1P –> dihydroxyacetone P and glyceraldehyde

- Defect: fructose intolerance (inhibits glycogenolysis and gluconeogenesis –> fasting hypoglycemia)

47
Q

Galactokinase

  • Galactose metabolism
  • Requires ATP
A

Galactose + ATP –> Galactose-1-P

- Defect: galactokinase deficiency (infantile cataracts)

48
Q

Aldose Reductase

- Galactose metabolism

A

Galactose –> galactitol

- too much galactitol –> cataracts

49
Q

Galactose-1-Phosphate Uridyltransferase

- Galactose metabolism

A

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

50
Q

HMG-CoA Synthase

- Ketogenesis (rate-limiting)

A

Makes ketone bodies during starvation

51
Q

Alcohol Dehydrogenase

  • Ethanol metabolism
  • NAD+ is limiting reagent
A

Ethanol + NAD+ –> Acetaldehyde + NADH

  • 0-order kinetics
  • Acetaldehyde is what causes hangover
  • Inhibited by Fomepizole (used for methanol or ethylene glycol poisoning)
52
Q

Acetaldehyde Dehydrogenase

  • Ethanol metabolism
  • NAD+ is limiting reagent
A

Acetaldehyde + NAD+ –> Acetate + NADH

- Inhibited by disulfiram (acetaldehyde accumulates –> hangover sx)

53
Q

ApoE

- Lipid transport

A

Mediates remnant uptake

54
Q

Apo A-1

- Lipid transport

A

Activates LCAT –> catalyzes esterification of cholesterol

- Nascent HDL –> mature HDL

55
Q

Apo C-II

- Lipid transport

A

Lipoprotein lipase cofactor

- Deficient in Type I (Hyperchylomicronemia)

56
Q

Apo B-48

- Lipid transport

A

Mediates chylomicron secretion

57
Q

Apo B-100

- Lipid transport

A

Mediates VLDL secretion

  • Binds LDL R
  • Defective binding in Type IIa (familial hypercholesterolemia)
58
Q

HMG-CoA Reductase

- Cholesterol synthesis (rate limiting step)

A

Converts HMG-CoA to mevalonate

  • Induced by insulin
  • Inhibited by statins
  • Cholesterol synthesis starts with acetyl CoA
59
Q

Acetyl CoA Carboxylase

- FA Synthesis (rate limiting step)

A
  • Cytoplasm of hepatocytes
60
Q

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

A
  • Mitochondrial matrix
61
Q

Phenylalanine Hydroxylase

  • Catecholamine synthesis/tyrosine catabolism
  • Cofactor: BH4
A

Phenylalanine –> Tyrosine

  • Tyrosine used to make thyroxine
  • Deficient: PKU
62
Q

Tyrosine Hydroxylase

  • Catecholamine synthesis/ tyrosine catabolism
  • Cofactor: BH4
A

Tyrosine –> Dopa

- Dopa used to make melanin

63
Q

Dopa Decarboxylase

  • Catecholamine synthesis/tyrosine catabolism
  • Cofactor: B6
A

DOPA –> Dopamine

- Inhibited by Carbidopa (rx for Parkinson’s)

64
Q

Dopa-beta-hydroxylase

  • Catecholamine synthesis/tyrosine catabolism
  • Cofactor: Vit C
A

Dopamine –> NE

Deficiency: nasal congestion, ptosis, orthostatic hypotension

65
Q

Phenylethanolamine-N-methyltransferase

  • Catecholamine synthesis/tyrosine catabolism
  • Cofactor: SAM (transfers methyl groups)
A

NE –> Epi

- Stimulated by cortisol

66
Q

Carbamoyl Phosphate Synthetase I

  • Urea cycle (rate-limiting step)
  • Requires ATP
A

CO2 + NH3 –> Carbamoyl phosphate

- In mitochondria

67
Q

Ornithine Transcarbamylase

- Urea cycle

A

Carbamoyl phosphate + ornithine –> citrulline

68
Q

Tyrosinase

- Catecholamine synthesis/tyrosine catabolism

A

Dopa –> melanin

- Deficiency: albinism

69
Q

Homogentisate Oxidase

- Catecholamine synthesis/tyrosine catabolism

A 
Homogentisic acid (from Tyr) --> maleylacetoacetic acid --> fumarate --> TCA cycle
- Deficiency: alkaptonuria (ochronosis, black urine)
70
Q

Cystathione Synthase

  • Homocysteine metabolism
  • Cofactor: B6
A

Serine + homocysteine –> cystathione

Deficiency: homocystinuria

71
Q

Methionine Synthase

  • Homocysteine metabolism
  • Cofactor: B12
A

Homosysteine –> methionine

Deficiency: homocystinuria

72
Q

Alpha-ketoacid Dehydrogenase

  • AA metabolism
  • Cofactors: thiamine pyrophosphate, lipoate, coenzyme A, FAD, NAD
A

Degrades branched AA (isoleucine, leucine, valine)

Deficiency: maple syrup urine disease

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