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Biochemistry > Porphyrins & Bile Pigments > Flashcards

Porphyrins & Bile Pigments Flashcards

1
Q

Bilirubin to bilirubinglucoronide

A

UDP glucoronyl transferase

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2
Q

Two (2) rxns of heme oxygenase system

A

(1) Iron is oxidized to ferric form (Fe3+) - HEMIN

(2) Hemin is reduced to HEME

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3
Q

Transports bilirubin to liver

A

Plasma albumin

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4
Q

Heme + heme oxygenase forms what?

A

Oxy-heme (closed tetrapyrrolic ring with iron)

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5
Q

Oxy-heme + heme reductase forms what?

A

Biliverdin (open tetrapyrrolic ring without iron)

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6
Q

Biliverdin + biliverdin reductase forms what?

A

Bilirubin (unconjugated, lipophilic)

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7
Q

Type of transport system in hepatocellular uptake of bilirubin

A

Facilitated transport system (carrier-mediated)

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8
Q

Intracellular transport of bilirubin in hepatocytes: Group of enzymes that represent 2% of cytosolic proteins

A

Ligandins

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9
Q

Intracellular transport of bilirubin in hepatocytes: Proteins that bind fatty acids

A

Z Protein

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10
Q

Three (3) sugars used in conjugation of bilirubin with glucoronic acid

A

Glucose (cell sap),
Xylose & Glucuronic Acid (formed from glucose by UDP-glucose)

Other agents eliminated by conjugation with glucuronic acid:
Steroids, thyroid hormones, catecholamines, estradiol, testosterone, bile acids, phenols, morphine

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11
Q

Enzyme in 1st step of glucuronidation of bile (glucose + ______ = UDPGA)

A

UDP-glucose dehydrogenase

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12
Q

Enzyme in 2nd step of glucuronidation of bile

A

Bilirubin-DUGAN-transferase (synthesized by microsomes)

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13
Q

Drugs that favor bilirubin conjugation and elimination

A

Phenobarbital, Antipyrine (microsomal enzyme inducers)

MOA: Increase bilirubin transferase activity

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14
Q

UDPGA + bilirubin + glucuronyl transferase = _______

A

Bilirubin mono- and di-glucuronides

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15
Q

Secondary to increased bilirubin (unconjugated) levels in the blood

A

Icterus/Icterisia (jaundice)

Elevated amts of conjugated bilirubin - obstructs biliary tree

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16
Q

Bilirubin conjugation/excretion capacity of liver

A

3000 mg per day (normal pdn of 300 per day)

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17
Q 
Type of jaundice associated with:
Sickle cell anemia,
Pyruvate kinase deficiency,
Glucose-6-phosphate deficiency,
Malaria
A

Hemolytic jaundice

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18
Q

Type of jaundice associated with:
Hepatic tumor,
Bile stones,
Biliary atresia

A

Obstructive jaundice (pale-colored stools)

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19
Q

Type of jaundice presenting with elevated SGOT (AST) and SGPT (ALT)

A

Hepatocellular jaundice

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20
Q

Enzyme associated with physiologic jaundice of the newborn

A

Hepatic bilirubin glucuronyl transferase (low levels at birth)

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21
Q

Occurs when elevated bilirubin levels exceeding the binding capacity of albumin and deposit into basal ganglia

A

Kernicterus (toxic encephalopathy)

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22
Q

MOA of phototherapy in jaundice (newborns)

A

Conversion of bilirubin to more polar, water-sol isomers (excreted into bile without conjugation to glucuronic acid)

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23
Q

Mg-containing porphyrin

A

Chlorophyll

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24
Q

Type I Porphyrin

A

Symmetric substitution

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25
Q

Type III Porphyrin

A

Asymmetric substitution

26
Q

Porphyrin linkage: 4 pyrrole rings through ____ or ____

A

Methyne or methenyl bridges

27
Q

Heme is synthesized from

A

Porphyrins and iron

28
Q

Heme is degraded into

A

Bile pigments and iron

29
Q

Gives red color to heme

A

Protoporphyrin

30
Q

Colorless compounds

A

Porphyrinogens

31
Q

Responsible for absorption and fluorescence in porphyrins

A

Double bonds joining pyrrole rings

32
Q

ALA dehydratase deficiency

A

ALA dehydratase-deficiency porphyria

33
Q

PBG deaminase deficiency

A

Acute intermittent porphyria

  • Most commonly occurring porphyria
  • Enzyme also called UPG synthase or hydroxymethylbilane synthase
34
Q

Uroporphyrinogen III synthase deficiency

A

Congenital erythropoietic porphyria (CEP)

  • Recessive
35
Q

Uroporphyrinogen decarboxylase deficiency

A

Porphyria cutanea tarda

36
Q

Coproporphyrinogen oxidase deficiency

A

Hereditary coproporphyria

37
Q

Protoporphyrinogen oxidase deficiency

A

Variegate porphyria

38
Q

Ferrochelatase deficiency

A

Protoporphyria

39
Q

Rate-controlling enzyme in heme synthesis

A

ALA synthase (d-aminolevulinic acid synthase)

40
Q

d-aminolevulinate formed from condensation of what substrates?

A

Succinyl-CoA and Glycine

  • ALA synthase enzyme
  • 1st rxn in heme synthesis
41
Q

Dimerization reaction between two (2) d-aminolevulinate molecules and catalyzed by ______ forming ______ and ______

A

Enzyme: ALA dehydratase (Zn-containing)
Product: Porphobilinogen, H2O

  • ALA dehydratase OR PBG synthase OR hydroxymethylbilane synthase
  • 2nd rxn in heme synthesis
42
Q

Enzymes catalyzing these condensation rxn:

(A) Porphobilinogen + H2O = hydroxymethylbilane
(B) Hydroxymethylbilane to uroporphyrinogen I
(C) Hydroxymethylbilane to uroporphyrinogen III

A

A. Uroporphyrinogen I synthase (PBG deaminase)
B. NONE; Non-enzymatic
C. Uroporphyrinogen III synthase + protein uroporphyrinogen II cosynthase

  • 3rd rxn in heme synthesis
43
Q

Uroporphyrinogen III to Coproporphyrinogen III, releasing CO2 (4 mol)

A

Uroporphyrinogen decarboxylase

  • decarboxylation rxn (acetate grps of UPG III to methyl)
  • 4th rxn in heme synthesis
44
Q

Coproporphyrinogen III to Protoporphyrinogen IX

A

Coproporphyrinogen III oxidase

  • requires O2
  • only acts on Type III
  • decarboxylation and oxidation of 2 proprionate residues
  • 5th rxn in heme synthesis (mitochondria)
45
Q

Protoporphyrinogen IX to Protoporphyrin IX

A

Proptoporphyrinogen III oxidase

  • requires molecular O2
  • oxidation rxn
  • 6th rxn in heme synthesis (mitochondria)
46
Q

Protoporphyrin IX to heme

A

Ferrochelatase OR heme synthase

  • insertion of iron into ring system
  • 7th rxn in heme synthesis (mitochondria)
47
Q

Important for detoxification

A

Hepatocytes

48
Q

Hepatic or erythroid?

A. ALA Synthase 1
B. ALA Synthase 2

A
  1. Hepatic - ALAS 1

2. Erythroid - ALAS 2

49
Q

Prevents ALAS 1 activity

A

Glucose and hemin

50
Q

Rate of heme synthesis (inc/dec) with diminished intracellular heme concentration and (high/low) levels of ALAS 1

A

Increases; Low

51
Q

Feedback inhibitor on ALA synthase

A

Hemin

  • Inhibits transport of ALAS from cytosol to mitochondria
  • Represses synthesis
52
Q

Characteristic absorption spectrum band in all porphyrins

A

Soret band

53
Q

Increased excretion of ____ and ____ in porphyrias

A

Coproporphyrins

Uroporphyrins

54
Q

Heme synthesis products measured in urine through spectrophotometry

A

ALA and PBG

55
Q

Three (3) treatments for porphyria

A

Glucose loading
Hematin
Beta-carotene

56
Q

Bilirubin conjugation

A

UDP glucoronyl transferase

57
Q

Biliverdin color

A

Blue green

58
Q

Colorless porphyrin

A

Urobilinogen

59
Q

Color of feces d/t

A

Stercobilin

60
Q

Only rxn in body to produce CO

A

Heme oxidation

Biochemistry (2 decks)

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