Question

Glutathione is a tripeptide found in most living cells. Partial hydrolysis yields Cys-Gly and Glu-Cys. What structures are possible for glutathione?

Short answer

The possible structure for glutathione, based on the partial hydrolysis results (Cys-Gly and Glu-Cys), is Glu-Cys-Gly. There are no alternative sequences for this arrangement that would satisfy the partial hydrolysis results.

Step-by-step solution

Identify the amino acids in the hydrolysis products

The partial hydrolysis products are Cys-Gly and Glu-Cys. This means that the three amino acids in glutathione are Cysteine (Cys), Glycine (Gly), and Glutamic acid (Glu).

Arrange the amino acids based on the partial hydrolysis results

We will use the two partial hydrolysis products to determine the order of the amino acids in the tripeptide glutathione.

Use the hydrolysis product Cys-Gly to arrange amino acids

The hydrolysis product Cys-Gly tells us that Cysteine and Glycine are directly connected in the peptide sequence. This gives us the starting point for the first scenario of our peptide sequence: 1. Cys-Gly

Use the hydrolysis product Glu-Cys to arrange amino acids

The hydrolysis product Glu-Cys indicates that Glutamic acid and Cysteine are directly connected in the peptide sequence. Considering this, we can now include Glutamic acid in our peptide sequence based on the result from step 3: 1. Glu-Cys-Gly

Confirm the arrangement and alternative sequences

Based on the information from the partial hydrolysis products, the only possible arrangement for the amino acids in the tripeptide glutathione is Glu-Cys-Gly. There are no alternative sequences for this arrangement that would satisfy the partial hydrolysis results. Therefore, the glutathione structure is: Glu-Cys-Gly