Heme Synthesis: Porphyrias Flashcards Preview

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Flashcards in Heme Synthesis: Porphyrias Deck (15):
1

What are the major tissues for heme synthesis?

Bone Marrow
Liver

2

Besides hemoglobin and myoglobin, heme can act as a prosthetic group of what enzymes?

Cyctochromes P450
Cytochromes of ETC
Catalase
Nitric Oxide

3

The four pyrrole rings of Heme are linked via what?

Methenyl Bridges

4

Which amino acid is used for heme synthesis?

Glycine

5

In regards to heme synthesis, succinyl CoA and glycine are used to form what?

Gamma-aminolevulinic acid (ALA)

6

What are the two isoforms of ALA? Where are they found? What regulates them?

ALA synthase 1 - liver
ALA synthase 2 - RBC
ALA 1 is inhibited by heme
ALA 2 is inhibited by low intracellular iron
Both require PLP, which can be inhibited by Isoniazid

7

Regarding heme syntheis, 2 ALA's form what in cytosol?

Porphobilinogen

8

What is used to form the linear hydroxymethylbilane (HMB)

4 porphobilinogens

9

Defiencies of ALAS2 leads to what disease?

Sideroblasticic anemia (x-linked)

10

The gene for ALAS2 is on which chromosome?

X-chromosome

11

Which enzyme combines to ALA to form porphobilinogen? What inhibits this enzyme?

ALA dehydrate (aka Porphobilinogen synthase)
Inhibited by: Lead
Note: Enzyme requires Zinc as cofactor

12

Which reaction does the PBG deaminase, or also known as HMB synthase, catalyze? What disease is related to the deficiency of this enzyme?

Combines 4 porphobilinogen to form hydroxymethylbilane.
Disease: Acute Intermittent Porphoria (NOT photosensitive)

13

Which of the diseases are related to severe photo-sensitivity in heme synthesis? Which enzyme is deficient?

1) Congenital Erythropoietic porphoria
Enzyme: UPG-3-synthase

2) Porphyria Cutanea Tarda
Enzyme: UPG-Decarboxylase

3) Erythropoietic Protophyria
Enzyme: Ferrochelatase

14

What is the treatment for porphyrias?

-Intravenous injection of glucose
-Hemin

15

Why is it a bad idea to administer barbituates to calm the patient down in Acute AIP?

Can lead to increased CYP450 synthesis and can worsen situation