Cysteine Metabolism

by Kevin Ahern, PhD

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    Now, homocystinuria, as I said, is pretty severe disease. It's a genetic disease caused by deficiency of this enzyme known as cystathionine beta-synthase. There are many problems that can arise in homocystinuria. There are musculoskeletal anomalies that occur, intellectual disabilities. And one of the reasons we have these intellectual disabilities is because of the problems with the nerve tissue in the brain. Seizures can result. There are numerous eye anomalies that can arise. Vascular disease because again, we have a lot of homocysteine that's occurring because it's not being converted into cysteine in the process. We see cystinuria which is an unrelated genetic disease that has many symptoms that are similar. We have the inability of the kidneys to reabsorb cysteine. So when this happens, then we see problems associated with the kidneys including high levels of cysteine, high levels of lysine, ornithine and arginine that appear in the urine. And because we have these things accumulating, we develop kidney stones that also occur. This is a not disease that you would wish on anyone. There are at least three other ways of making cysteine and I illustrate these here. One of these comes from serine directly. In this process, acetylcholine gets -- It donates an acetyl group to serine to make O-acetyl L-serine. That is shown here. And the next step of the process, the sulfur that ends up being cysteine comes with the addition of a hydrogen sulfite. This splits out the acetate in the process leaving behind cysteine for making proteins. A second way of making cysteine actually comes from proteins itself. One of the things that cysteine can do on a protein is combine with another cysteine in a covalent bond to make this dicysteine as it were called L-cysteine. This involves the joining of...

    About the Lecture

    The lecture Cysteine Metabolism by Kevin Ahern, PhD is from the course Amino Acid Metabolism. It contains the following chapters:

    • Cysteine Metabolism & Health
    • Selenocysteine Metabolism

    Included Quiz Questions

    1. It is closely linked to methionine metabolism.
    2. It requires hydrogen sulfide.
    3. It can occur from arginine.
    4. It cannot occur from serine.
    5. None of the answers are correct.
    1. All of the answers are true.
    2. It is made on a tRNA.
    3. It is incorporated into proteins in an unusual fashion.
    4. It does not have a codon in the genetic code.
    5. None of the answers are true.

    Author of lecture Cysteine Metabolism

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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