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2010-10-21 21:46:13
Enzymes Metabolism

The ezymes and other info for exam 4
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  1. Function of HMG CoA synthase?
    • Cholesterol Synthesis
    • Function: Catalyzes the creation of HMG CoA from acetyl CoA and NADPH
    • First step in cholesterol synthesis
  2. Function of HMG CoA reductase?
    3 ways it is regulated?
    • Cholesterol Synthesis
    • *Rate limiting step in cholesterol synthesis.
    • Function: Catalyzes the reducing reaction of HMG CoA to mevalonic acid
    • Regulated:
    • 1. SREBP, which is released from the ER when cholesterol levels are low
    • 2. High cholesterol decreases it (by ruining stability of mRNA)
    • 3. Hormonally, insulin activates it by dephosphorylating it, glucagon deactivates by phosphorylating
  3. Function of Cholesterol 7-alpha-hydroxylase?
    • Bile acid synthesis from cholesterol
    • Rate limiting step in bile acid synthesis
    • Function: converts cholesterol to an intermediate that is then converted to primary bile acids (cholic acid or chenodeoxycholic acid)
  4. Function of Lipoprotein Lipase (LPL)?
    Activated by?
    • Lipoprotein Metabolism
    • Function: degrades tryacylglycerols in adipose tissue
    • Activated by: Apo C-II, insulin (fed state)
  5. Function of hepatic lipase?
    Function: catabolyses IDL back into LDL
  6. Function of acyl CoA cholesterol acyl transferase (ACAT)?
    Activated by?
    • Function: esterifies cholesterol to cholesterol ester for storage
    • Activated by: increased intracellular cholesterol
  7. Function of phosphatidylcholine cholesterol acyl transferase (PCAT)?
    Activated by?
    • Function: Esterifies cholesterol to cholesterol esters in HDL
    • Activated by: Apo A-I of HDL
  8. Function of glutathione peroxidase?
    • Reduction of hydrogen peroxide
    • Funcion: catalyzes the degredation of H2O2 (hydrogen peroxide) with reduced glutathione (G-SH) to H2O and oxidized glutathione (GS-SG)
  9. Function of Glutathione reductase?
    • Reduction of hydrogen peroxide
    • catalyzes reaction of oxidized glutathione to reduced glutathione (G-SH), NADPH donates electrons
  10. Function of glucose 6-phosphate dehydrogenase (G6PD)?
    Function? catalyzes creation of NADPH
  11. Function of superoxide dimutase (SOD)?
    Function: catalyzes reaction that destroys oxygen free radicals
  12. Function of cytochrome b5 reductase?
    • Methoglobin to hemoglobin
    • Function: converts oxidized cytochrome b5 back to its reduced form (using NADH as and electron donor)
  13. Function of cytochrome b5 oxidase?
    • Methemoglobin to hemoglobin
    • Function: catalyzes the reaction of reducing methemoglobin back to hemoglobin (cytochrome b5 is an electron donor)
  14. Function of alcohol dehydrogenase?
    • Ethanol oxidation
    • Function: catalyzes oxidation of ethanol to acetaldehyde (transfers electrons to NAD+ to make NADH in cytosol)
  15. Function of aldehyde dehydrogenase?
    • Ethanol oxidation
    • Function: oxidizes acetaldehyde (from ethanol) into acetate (donates an electron to NAD+ to form NADH in the cytosol)
  16. Function of CYP2E1?
    Induced by?
    • Ethanol oxidation
    • Function: oxidizes ethanol to acetaldehyde and NADPH to NADP+
    • Induced by: chronic ingestion of ethanol
  17. Function of aminotransferase?
    Where is it found?
    • Amino acid catabolism
    • Function: funnels nitrogen from amino acids into glutamate (alpha-amino acid to alpha-keto acid--> enters TCA cycle)
    • Found in: liver, kidney, intestine, muscle
  18. Function of glutamate dehydrogenase?
    • Amino acid catabolism
    • Function: removes the amino group from glutamate to form free ammonia (oxidative deamination), NADH, and alpha-ketoglutarate
  19. Function of alanine aminotransferase (ALT)?
    • Amino acid catabolism
    • Function: catalyzes the transfer of the amino group from alanine to alpha-ketoglutarate to form pyruvate and glutamate (forms most of the pyruvate used for gluconeogenesis)
  20. Function of aspartate aminotransferase (AST)?
    • Amino acid catabolism (urea cycle)
    • Function: during amino acid catabolism glutamate is used to make apartate from oxaloacetate (OAA) to run the urea cycle (AST is an exception to the rule)
  21. Function of carbamoyl phosphate synthetase I (CPSI)?
    • Urea synthesis
    • Function: rate limiting step in urea synthesis, catalyzes formation of carbamoyl phosphate from ammonia, takes 2 ATP and CO2
    • Activator: High ammonia production, N-acetylglutamate, high protein diet
    • Inhibitor: Protons, low protein diet
  22. Function of arginase?
    • Urea synthesis
    • Function: hydrolyzes arginine to form urea and regenerate ornithine
  23. Function of carbamoyl phosphate synthetase II (CPSII)?
    • Pyrimidine synthesis
    • Function: catalyzes reaction that synthesizes pyrimidine in cytosol
  24. Function of N-acetylglutamate sythase?
    Activated by?
    • Function: catalyzes the sythesis of N-acetylglutamate (which activates CPSI)
    • Activated by: increased concentration of acetyl CoA, and arginine
  25. Function of glutamine sythetase?
    Function: converts left over ammonia into glutamine (lower Km for ammonia than CPSI, located downstream of the urea cycle in the liver to catch left over ammonia)
  26. What are the branch chain amino acids (BCAAs)?
    leucine, isoleucine and valine
  27. How are the urea cycle and gluconeogenesis corelated?
    • when gluconeogenesis decreases so does the urea cycle,
    • when gluconeogenesis increases so does the urea cycle
  28. Function of BCAA aminotransferase?
    Where is it?
    Activated by?
    • BCAA catabolism
    • Function: generates BC alpha-keto acids and funnels the nitrogen into glutamate
    • Where: muscle and brain
    • Activated: high protein diet (for nonessential amino acids)
  29. Function of branch chain (BC) alpha-keto acid dehydrogenase (BCKD)?
    Activated by?
    Inhibited by?
    • BCAA catabolism
    • Function: Rate limiting step in BCAA catabolism, catalyzes oxidative decarboxylation of all three branch chain alpha-keto acid dehydrogenase complexes (requires thiamine, riboflavin, niacin, pantothenic acid, and lipoic acid)
    • Activated: dephosphorylation, increase in BCAAs, high protein diet
    • Inhibited: phosphorylated, decrease in BCAAs, low protein diet
  30. What are the fates of the BCAAs?
    • Leucine (ketogenic): acetoacetate and acetyl CoA
    • Valine (glucogenic): succinyl CoA
    • Isoleucine (glucogenic and ketogenic): acetyl CoA and succinyl CoA
  31. Function of tyrosin hydroxylase?
    Activated by?
    • Catecholamine sythesis
    • Function: catalyzes hydroxylation of tyrosine to DOPA, rate limiting step for catecholamine synthesis (also first step)
    • Requires: tetrahydrobiopterin for an electron
    • Activated by: calcium/calmodulin dependent protein kinase (phophorylates it), nerve stimulation, persistant neuronal activity
  32. Function of aromatic amino acid decarboxylase (AADC)?
    • Catecholamine Synthesis
    • Function: catalyzes the decarboxylation of DOPA to form dopameine
    • Requires: vitamin B6
  33. Function of dopa beta-hydroxylase (DBH)?
    Activated by?
    • Catecholamine synthesis
    • Function: catalyzes the hydroxylation of dopamine to norepinephrine
    • Requires: vitamin C and O2
    • Activated by: cortisol, presistant neuronal activity
  34. Function of phenylethanolamine-N-methyltansferase (PNMT)?
    Enhanced by?
    • Catecholamine synthesis
    • Function: catalyzes the cytosolic N-methylation of norepinephrine to form epinephrine
    • Requires: S-adenosylmethionine (SAMe) as a methyl donor
    • Enhanced by: cortisol
  35. What is the function of DAT, NET, and SERT?
    They are monoamine reuptake proteins that return most of the released monoamines (dopamin, norepinephrine, seretonin) to the presynaptic side
  36. What is the function of VMAT-2?
    Moves catecholamines, especially dopamine into vesicles
  37. Function of monoamine oxidase (MAO)?
    • Catecholamine degredation
    • Function: deaminates (inactivates) catecholamines (in outer membrane of mitochondria in intestine and liver)
  38. Function of catechol-O-methyl transferases (COMT)?
    • Catecholamine degredation
    • Function: adds a methyl group to catecholamines to inactivate them (in liver and kidney)
  39. What are purines?
    Examples in DNA and RNA?
    • 9-membered bicyclic planar, aromatic rings
    • DNA and RNA: Adenine (A), Guanine (G)
  40. What are pyrimidines?
    Examples in DNA and RNA?
    • 6-membered planar, aromatic rings
    • DNA and RNA: Cytosine (C)
    • DNA only: Thymine (T)
    • RNA only: Uracil (U)
  41. What is a nucleoside?
    A nitrogenous base and a sugar
  42. What is a nucleotide?
    A phosphorylated nucleoside
  43. What are the 6 functions of nucleotides?
    • 1. Building blocks for nucleic acids
    • 2. Activated intermediates for glycogen
    • 3. Second messengers in signal transduction
    • 4. Structural components of cofactors
    • 5. Enzymes that process RNA
    • 6. Energy currency within the cells
  44. Function of PRPP synthetase?
    Activated by?
    Inhibited by?
    • Purine nucleotide synthesis
    • Function: Rate limiting step in purine and pyrimidine nucleotide biosynthesis, catalyzes the transfer of a phosphate group from ATP to ribose-5-P to form PRPP (activated sugar)
    • Activated by: inorganic phosphate
    • Inhibited by: purine and pyrimidine nucleotides
  45. Function of glutamine-PRPP amidotransferase?
    Activated by?
    Inhibited by?
    • Purine nucleotide sythesis
    • Function: first commuted step, replaces the phosphate group of PRPP with the amide nitrogen of glutamine
    • Activator: PRPP (substrate)
    • Inhibitor: purine nucleotides (AMP, GMP, IMP)
  46. Explain the major points of IMP formation?
    • Purine nucleotide synthesis
    • 1. requires a significant amount of ATP
    • 2. Needs a folate (folic acid deficiency causes anemia)
    • 3. It is the first recognizable purine after all the steps
    • 4. There are many steps catalyzed by multifunctional enzymes (copy machine)
  47. What are the inhibitors and activators of the conversion of IMP to AMP?
    • Inhibitor: AMP
    • Activator: GTP
  48. What are the inhibitors and activators of the conversion of IMP to GMP?
    • Inhibitors: GMP
    • Activators: ATP
  49. Function of adenylate kinase?
    Converts AMP to ADP
  50. Function of guanylate kinase?
    Converts GMP to GDP
  51. Function of ATP synthase?
    Converts ADP to ATP
  52. Function of hypoxathine-guanine phosphoribosyltransferase (HGPRT)?
    • Salvaging of purine nucleotides
    • Function: responsible for most recycling (salvaging) of purines, converts PRPP back into GMP
  53. Function of adenosine deaminase?
    • Purine degredation
    • Function: removes amino group from AMP to form IMP, or removes amino group from adenosine to form inosine
  54. Function of xanthine oxidase?
    • Purine degradation
    • Function: catalyzes the last two steps in purine degradation, oxidation of hypoxanthine and xanthine to uric acid
  55. What is hyperuricemia?
    Abnormally high plasma (or serum) monosodium urate concentration
  56. What percentage of patients with gout have hyperuricemia?
    100%, gout is caused by many years of hyperuricemia, not all patients with hyperuricemia have gout though
  57. Define tophi?
    monosodium urate crystal formations
  58. What three factors is the solubility of monosodium urate dependent on?
    • 1. concentration of ions of urate and sodium
    • 2. temperature
    • 3. pH
  59. What causes primary gout?
    Overproduction of uric acid (urate), 24-hour urine analysis will show uric acid production greate than normal
  60. What are 4 main causes leading to hyperuricemia and gout?
    • 1. decrease in HGPRT activity
    • 2. Overactive PRPP synthetase
    • 3. Increased rate of purine degredation
    • 4. Increased cell death
  61. What is the main drug used to treat primary gout and what enzyme is it a substrate for and inhibits?
    • Drug: Allopurinol
    • Enzyme: Xanthine oxidase (it is a substrate for xanthine oxidase and after being converted to alloxanthine it inhibits xanthine oxidase as well)
  62. What is secondary gout?
    Underexcretion of urate
  63. Which amino acid is the major provider of one-carbon units in the body?
    Serine (glycine and histidine also donors of one-carbon units for one carbon metabolism)
  64. What are the three parts in the structure of folic acid?
    • 1. pteridine ring
    • 2. p-aminobenzoic acid (PABA)
    • 3. one glutamic acid residue
  65. What causes homocysteinuria?
    A defect in the rate-limiting enzyme cystathione synthase, which is a defect in the transsulfuration pathway. (causes problems in eye, CNS, skeletal, and vascular system)
  66. What is transsulfuration?
    The creation of cysteine from homocysteine
  67. What are the pro-apitite hormones from the hypothalamus?
    • ghrelin (stomach)
    • neuropeptide y (brain)
  68. What are the pro-satiative hormones from the hypothalamus?
    • GLP-1
    • cholecystokinin (intestine)
    • leptin (adipose)
  69. What does glutamate being taken up by the astrocytes do to the rate of glycolysis? Why?
    It increases the rate of glycolysis, glucose uptake, phosphorylation, and catabolism (caused by an decrease in ATP and and increase in ADP which stimulates PFK-1)
  70. What is von Gierke disease?
    Type I glycogen storage disease (G6Pase deficiency), defect in G6Pase because inability to dephosphorylate it which impairs glucose release from the liver, patients have hypoglycemia between meals