Tuesday, March 17, 2015

Heme synthesis mnemonic

Hey everyone! Long time no see!
Today we'll be learning about heme synthesis.

The biosynthesis of heme mnemonic 
1. The heme ring system is synthesized from glycine and succinyl-CoA in the mitochondria.
d-Aminolevulinate Synthase (ALA Synthase, ALAS) is the rate-limiting step. Pyridoxal phosphate is the coenzyme.

Mnemonic: "Alas! Mighty dracula sucks blood with glistening phoshorous teeth."
Alas! (ALA synthetase enzyme)
Mighty (Mitochondria)
Dracula (d-ALA)
Sucking (Succinyl CoA)
Blood (Heme synthesis)
Glistening (Glycine)
Phosphorous (Pyridoxal phosphate coenzyme)

2. PBG Synthase (Porphobilinogen Synthase), also called ALA Dehydratase, catalyzes condensation of two molecules of d-aminolevulinic acid (ALA) to form porphobilinogen (PBG). This step is inhibited by lead.

Mnemonic: "This leads to dehydration of poor Billy."
Leads (Pb inhibits this step)
To (Two molecules of d-ALA)
Dehydration (ALA dehydratase)
Poor Billy (Porphobilinogen)

3. After that, I remember "UCP" (UnCouplers of oxidative phosphorylation) for the next three substrates:
Uroporphyrinogen
Coproporphyrinogen
Protoporphyrinogen

(Alternatively: "Urine, crap, poop")

4. Protoporphyrinogen is acted upon by Ferrochelatase which incorporates iron to produce heme. 

Mnemonic: "PharoaH"
P: Protoporphyrinogen
H: Heme
Pharoah sounds like "Ferro" for Ferrochelatase

This step is inhibited by lead too. 
Mnemonic: "Latase Likes Lead. "

From vampires to mummies, our heme journey ends here.

Here are a few of my ugly old notes. I didn't spend much time explaining them because I doubt they'll be helpful. I uploaded them anyway :)

The heme synthesis pathway (Notes) 
Heme notes, zoomed in 

What the short forms in the notes stand for -
AIP: Acute Intermittent Porphyria
CEP: Congenital erythropoietic protoporphyria
PCT: Porphyria cutanea tarda
HCP: Hereditary coproporphyria
VP: Varlegate porphyria
EPP: Erythropoietic protoporphyria

That's all!

Made this post specially on request by Anonymous, hope this helps you :) 

-IkaN

11 comments:

  1. The porphyria at the last step is given as Hereditary protoporphyria in my book? Also PBG deaminase deficiency causes AIP.

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    Replies
    1. The deficient enzyme in AIP is porphobilinogen deaminase (PBGD), also known as hydroxymethylbilane synthase (HMB synthase). This enzyme was formerly known as uroporphyrinogen I-synthase, and this term is still used by some clinical laboratories.

      Delete
    2. I don't know about the hereditary protoporphyria thingy.

      I only found resources mentioning EPP on the internet when I tried Google - ing Ferrochelatase deficiency. Probably different names for the same thing?!

      Delete
    3. Ok, thanks for the info...and urine,crap,poop was epic, as was the dracula mnemonic. :)

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  2. Thanks for this page. Huge help! May I add for the conversion of protoporphyrinogen to heme happens in the mitochondria. I thought "Mighty PharaoH" was quite appropriate to tie everything together, just like might dracula.

    ReplyDelete
    Replies
    1. Thanks for the extra mnemonics :)

      Delete

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