Which of the following is not one of the three amino acids that make up glutathione?

Glutathione is a tripeptide composed of three specific amino acids: cysteine, glutamate, and glycine. These amino acids come together to form this important antioxidant that plays a critical role in protecting cells from oxidative stress and maintaining cellular health.

Cysteine is the key amino acid in glutathione, as it contains a sulfhydryl group (-SH) that is crucial for the antioxidant activity of glutathione. Glutamate, also known as glutamic acid, contributes to the structure of glutathione and helps in the synthesis of proteins. Glycine acts as the third component of this tripeptide, helping to stabilize the molecule and allow it to function properly.

Tryptophan, on the other hand, is not part of glutathione's structure. It is an essential amino acid involved in the production of various proteins and neurotransmitters, such as serotonin, but it does not contribute to the formation of glutathione. This distinction makes it clear why the correct choice is the amino acid not involved in the composition of glutathione.