Draw the structure of a tripeptide glutathione with the following amino acid residues: Glu-Cys-Gly. What is the net charge of the tripeptide?

Question

At physiological pH?

Answer 1

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The image below shows the form of the molecule in its unionized form. At physiological pH, the alpha-amino group of the glutamyl residue is protonated and positively charged, and the two carboxyl groups (the terminal one of glycine and the alpha-carboxyl group of the glutamyl residue) are both ionized and negatively charged. Thus the molecule has a net charge of -1 at physiological pH.