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MCM > Heme synthesis and degradation > Flashcards

Heme synthesis and degradation Flashcards

1
Q

describe the structure of the heme

A

poryphyrin 5-membered ring complex N atoms face the Fe2+

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2
Q

where is heme synthesized?

A

liver and erythroid cells of bone marrow

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3
Q

what are the three phases of heme synthesis?

A

1-mitochondria-make ALA from Gly and succinyl CoA
2-cytosol-2ALA combine to PBG, 4 of these make CPP3
3-mitochondria-two oxygenation rxn to install side chain=protoporphyrinogen9 and make conjugated ring, insertion of Fe2+

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4
Q

What is ALA?

A

in mitochondria: delta-aminolevulinic acid (ALA synthase)

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5
Q

What is CPP3?

A

coproporphyrinogen 3-cytosol to mitochondria (uro.. dehydrogenase 3)

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6
Q

What is PBG?

A

porphobilinogen-cytosol (ALA dehydrogenase)

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7
Q

Describe ALA synthase

A

needs B6 (pyridoxal phosphate or PLP)
2 isoforms ALAS1(ubiquitous) and ALAS2 (erythroid cells)
Heme inhibits (feedback)
Iron increases transcription and translation
Decarboxylation rxn

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8
Q

What are the 4 most important enzymes to know regarding heme synthesis? Where are they located?

A

ALA synthase mito
ALA dehydrogenase cyto
Porphobilinogen deaminase cyto
Ferrochelatase mito

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9
Q

What enzymes does Pb interact with? What molecules accumulate?

A

ALA dehydratase
ferrochelatase
ALA and Protoporphyrin IX accumulate

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10
Q

What enzymes can have a defect and cause a porphyria?

A 
ALA synthase
porphobilinogen deaminase
uroporphyrinogen 3 cosynthase
uroporphyrinogen decarboxylase
protoporphyrinogen oxidase
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11
Q

What type of poryphria would a defect in PBG deaminase (liver) cause?

A

Acute intermittent hepatic

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12
Q

What type of poryphria would a defect in uroporphyrinogen 3 synthase (erythrocytes) cause?

A

congenital

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13
Q

What type of poryphria would a defect in uroporphyrinogen decarboxylase cause?

A

porphyria cutanea tarda
most common
hepatoerythropoietic

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14
Q

What type of poryphria would a defect in protoporphyrinogen IX oxidase cause?

A

Variegate porphyria

hepatic

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15
Q

What phenotype is attributed to a deficiency in uroporphyrinogen 3 synthase?

A

a build-up of uroporphyrinogen I

red in urine, red flourescence in teeth, skin photosensitivity

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16
Q

What enzyme is involved in generating bilirubin from heme?

A

heme oxygenase cleave the cycle and makes it into a linear form
requires oxygen,

17
Q

Describe biliverdin synthesis

A

heme oxidase

iron oxidized from ferrous to ferric

18
Q

What is the second eznyme involved in bilirubin synthesis?

A

biliverdin reductase

eliminates double bond

19
Q

Describe free BR

A

unconjugated/indirect (insoluble)

bound to albumin

20
Q

Describe direct BR

A

conjugated with glucoronic acid (soluble)

21
Q

describe conjugation

A

UDP glucose converted to UDP-glucuronic acid
UDP-glu transferase conjucate free BR and UDPGlu acid
does this twice to add two sugars (X2)

22
Q

What is the rate limiting step of BR removal?

A

UDP glucuronyl transferase

23
Q

What form is iron in heme? What form does it take after the action of heme oxygenase?

A

In Hb it is ferrous (Fe2+)

after oxygenase it is ferric (Fe3+)

24
Q

What is the cause of green pigmentation in heme breakdown?

A

conversion of ferrous to ferric

Fe2+ to Fe3+

25
Q

What carries bilirubin in the blood?

A

albumin

26
Q

What steps are needed and where in BR excretion?

A

BR->urobilinogen in intistine
urobilinogen taken by kidney->urobilin
urobilinogen stays in gut->stercobilin

27
Q

what are characteristics of pre-hepatic jaundice?

A

hemolytic anemias
liver cannot uptake excrete, or conjugate
fetal incompatability
glucose 6 phosphate dehydrogenase deficiency

28
Q

What are findings of pre-hepatic jaundice?

A 
elevated unconjugated BR in blood,
normal conjugated levels
normal serum levels
urobilinogen in urine
direct BR not in urine
29
Q

What are findings in intra-hepatic jaundice?

A

unconj and conj BR level=depends
increase in serum ALT and AST levels
urobilinogen levels in urine is normal
conjugated BR in urine

30
Q

Describe characteristics of post-hepatic jaundice

A

BR cannot be excreted

bile might not flow

31
Q

What are findings in post-hepatic jaundice?

A

elevated conjugated BR levels in blood
normal AST and ALT levels
conjugated BR is present in urine (dark)

32
Q

describe neonatal jaundice

A

elevation of

33
Q

describe neonatal jaundice

A 
elevation of un-conjugated BR
deficiency of UDP-GT enzyme
breakdown of fetal Hb, replaced with adult Hb
BR can cause encephalopathy`
varies in severity due to causes
34
Q

What does phototherapy do?

A

blue fluorescent light causes BR to convert to more soluble isomers
also heme oxygenase inhibitor may be used

MCM (10 decks)

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