Re: does glutathione have more than2 peptide bonds?

Hi Claire,

As you can see from the figure below, glutathione only has 2 peptide bonds.

Glutathione is a tripeptide that is synthesized by forming one peptide bond between the gamma-carboxyl group of glutamate and the amino group of cysteine (forming gamma- glutamyl cysteine), and then by forming a second peptide bond between the carboxyl group of cysteine and the amino group of glycine. In the figure above, those portions of glutathione that come from each of these amino acids is color coded, and the two peptide bonds are shown in black and indicated.

I'm not sure exactly how you are carrying out the Biuret Test, but this test indicates the presence of peptide bonds with a blue to violet color change. However, the dramatic violet color is only observed in the presence of long peptides (proteins), and a pink color change is seen in the presence of short peptides. As a tri-peptide, glutathione may be too short for the pink color to be obvious without the use of a spectrophotometer (or some other sort of machine that can quantify color changes).

This information on glutathione came from the textbook "Biochemistry", by Lubert Stryer,