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Heme Synthesis

by Kevin Ahern, PhD
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    Now, in going through heme synthesis, what's remarkable is how we can start with very simple molecules and make the complex heme ring as we will see. The first step of the synthesis begins with the simple compound, succinyl-CoA and glycine. Succinyl-CoA is from the citric acid cycle and glycine is a simple amino acid. The combining of these two molecules together creates aminolevulinic acid. The first intermediate on the way to making heme. This reaction is a decarboxylation that releases both the carbon dioxide and the Co-A part of the molecule as we see here. The enzyme catalyzing this reaction is aminolevulinic acid or ALA synthase as we call it. ALA synthase is found in almost all non-plant eukaryotes and also in some bacteria. Now the enzyme is found in the mitochondria and that's important because that's where the succinyl-CoA is located. The synthesis of the enzyme is tightly controlled by the presence of iron binding proteins. We don’t want to be making this if iron is not available. So, if iron binding proteins are abundant, that means there's iron to put in and make heme. The second step in the process of making heme involves the condensation of two of these molecules of aminolevulinic acid. The product to this reduction creates porphobilinogen as you can see here. And we already start to see complex molecules resulting from these interactions. This reaction splits out two molecules of water and it's catalyzed by the enzyme porphobilinogen synthase. Porphobilinogen synthase is sensitive to magnesium concentration and also to pH. It's also very easily inactivated by heavy metals. And because of this, it is actually the source of our sensitivity in our body to lead poisoning. When you heard lead poisoning, it's affecting this enzyme. And that's pretty severe as you can...

    About the Lecture

    The lecture Heme Synthesis by Kevin Ahern, PhD is from the course Amino Acid Metabolism.


    Included Quiz Questions

    1. It starts with glycine and succinyl-CoA.
    2. It begins with a cytoplasmic enzyme.
    3. It begins with the incorporation of carbon dioxide.
    4. None of the answers are true.
    5. All of the answers are true.
    1. ...two glycines and two succinyl-CoAs would be required.
    2. ...a ring structure is destroyed.
    3. ...the enzyme is actually stimulated by heavy metals.
    4. None of the answers are true.
    5. All of the answers are true.
    1. Ammonia is released during this process.
    2. six glycines and six succinyl-CoAs would be required
    3. increased production results in a type of porphyria
    4. All of the answers are true.
    5. None of the answers are true.
    1. It is the first cyclic intermediate in heme synthesis.
    2. Its synthesis requires input of water.
    3. It is in excess with congenital erythropoietic porphyria.
    4. All of the answers are true.
    5. None of the answers are true.
    1. None of the answers are true.
    2. It decarboxylates coproporphyrinogen III.
    3. It is a methodical enzyme, working very slowly.
    4. It uses four carbon dioxide molecules.
    5. All of the answers are true.
    1. The enzyme catalyzing its formation is in the mitochondrion.
    2. Two molecules of coproporphyrinogen III are used during this process.
    3. The enzyme uses magnesium in catalysis.
    4. All of the answers are true.
    5. None of the answers are true.
    1. All of the answers are true.
    2. It is a precursor of heme and chlorophyll.
    3. It is formed in an oxidation reaction.
    4. It is formed in a reaction catalyzed by an inner mitochondrial enzyme.
    5. None of the answers are true.
    1. It requires electronic rearrangement for its final form.
    2. All of the answers are true.
    3. It is formed by catalysis of ferrocatalase.
    4. It is formed as Heme C and other hemes are made from it.
    5. None of the answers are true.

    Author of lecture Heme Synthesis

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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