Pyruvate Family: Alanine Metabolism

by Kevin Ahern, PhD

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    00:01 The next family of amino acids whose metabolism we will consider is that of the pyruvate family.

    00:07 Now, pyruvate metabolism is tied very closely to the amino acid alanine.

    00:12 And we see again transamination appearing as a very important consideration.

    00:16 Transamination of pyruvate is what leads to the production of alanine.

    00:21 The donor in this case of the amine group is glutamate as we've seen for other reactions.

    00:26 And the enzyme involved in this is alanine transaminase.

    00:30 We can see that, of course, the amine comes from glutamate, goes on to make alanine.

    00:34 Pyruvate's oxygen is what makes the alpha-ketoglutarate on what was originally glutamate.

    00:41 Alanine is a byproduct of the catabolism of valine, leucine and isoleucine as well.

    00:47 So, break down of those amino acids is an alternate way of making alanine.

    00:52 Alanine is a very important molecule for managing the movement of amines in the body.

    00:57 This occurs as a result of the glucose-amine -- I'm sorry, the glucose-alanine cycle which I will show here.

    01:04 So, the glucose-alanine cycle overlaps with the cori cycle.

    01:07 And they are both shown in this figure right here.

    01:09 The cori cycle on the right and the glucose-alanine cycle on the left.

    01:13 They have in common the features that are shown in the center.

    01:16 So to describe these pathways, I want to show a little bit about what's happening in the individual conditions.

    01:22 If we start in the bloodstream with the glucose, glucose goes to tissues that need it.

    01:27 I've picked muscle here as an example, but we could be talking about brain as well.

    01:31 When cells are breaking down glucose and there's a lack of oxygen, they will go in this cycle to the right.

    01:38 Now, that's important in rapidly metabolizing muscles tissue for example.

    01:43 And these circumstances, ammonia concentration is probably fairly low.

    01:48 When that happens, pyruvate is converted into lactate because the oxygen is commonly limiting.

    01:53 Lactate is taken from those tissues and moved back to the bloodstream and ultimately to the liver where it is converted back to pyruvate and then ultimately made back into glucose for additional energy for those tissues that need it.

    02:06 Other conditions where we have high ammonia however, a different circumstance happens.

    02:10 Now this might happen in muscle.

    02:11 It might more commonly happen in brain because is very sensitive to the high ammonia levels that can be produced.

    02:19 So if that happens, pyruvate is converted into alanine by a transamination reaction.

    02:25 That movement of that amine out of the brain is very, very important.

    02:30 That transaminaton that I've just showed is the one that's most commonly done to produce this.

    02:36 Alanine produced in this way is dumped into the bloodstream and alanine is then taken to the liver where it's converted back to pyruvate and that amine group is converted ultimately into urea.

    02:48 Now, this turns out to be important because glutamate, which is a way of mopping up that amine group that I've talked about, is a neurotransmitter.

    02:56 So for talking about the brain, we really don't want to be moving that neurotransmitter out of the brain.

    03:01 Putting it on to alanine and letting alanine carry it to the liver is a more important consideration.

    03:05 So having alanine carry the amine is a very, very important part of the glucose-alanine cycle.

    03:12 The transamination in the liver now is removing the amine and that amine then is put on to making urea, and urea is the way that we excrete that excess amine.

    03:23 Breakdown a glutamate therefore yields amine for a urea production.

    About the Lecture

    The lecture Pyruvate Family: Alanine Metabolism by Kevin Ahern, PhD is from the course Amino Acid Metabolism.

    Included Quiz Questions

    1. They all have non-polar R groups
    2. They all have alanine as a precursor
    3. They are not important in the glucose-alanine cycle
    4. All of the answers are true
    5. None of the answers are true
    1. None of the answers are true
    2. Transamination does not occur
    3. Gluconeogenesis does not occur
    4. Glycolysis does not occur
    5. All of the answers are true
    1. ...α-ketoglutarate and alanine.
    2. None of the answers are correct.
    3. ...aspartate and glutamate.
    4. ...aspartate and alanine.
    5. ...asparagine and alanine.

    Author of lecture Pyruvate Family: Alanine Metabolism

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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