Heme Metabolism Flashcards
What is the general structure of the heme ring?
It is made of 4 pyrrole groups and an iron atom
What is the 1st step of heme synthesis?
Succinyl CoA + Glycine -> ALA
What is the rate limiting step of heme synthesis?
The 1st step to generate ALA
What is the enzyme catalyzing the 1st step of heme synthesis?
ALA Synthase
What is the 2nd step of heme synthesis?
2 ALA -> Porphobilinogen
What is the difference between porphyrinogens and porphyrins?
Porphyrinogens have no double bonds at the bridging carbons and are colorless.
Porphyrins have double bonds at the bridging carbons and have colors and are highly fluorescent.
What can happen to porphrinogens upon light exposure?
They can be converted into porphyrins via non-enzymatic oxidation
What is ALA synthase regulated by?
Heme will inhibit the action of ALA synthase
What is the mechanism of disease in acute intermittent porphyria?
It is caused by a deficiency of porphobilinogen deaminase.
This results in ALA build up which is toxic to neurons. The lack of heme formation will also shut off the negative feedback and exacerbate the disease as well.
What is the mechanism of disease in variegate porphyria?
Deficiency of protoporhyrinogen oxidase.
This causes a build up of porphyrinogen intermediates which can be converted into porphyrins via light and will damage the skin as a result.
What are the products of hemoglobin metabolism?
- Heme
- Globin
What does heme from hemoglobin eventually degrade to?
Bilirubin
Fe (reused)
What does globin from hemoglobin eventually degrade to?
Free amino acids
What breaks down the cyclic structure of heme?
Heme oxygenase
What is unconjugated bilirubin?
It is also known as indirect bilirubin and it is insoluble.
It complexes with albumin in the blood to be carried to the liver
