Incorrect statement about \(\alpha\)-amino acids of proteins among the following is

Methionine is an essential amino acid, so the first statement is correct.

Glycine is the simplest amino acid with the formula \(H_2N-CH_2-COOH\). Since its \(\alpha\)-carbon is attached to two identical hydrogen atoms, it is achiral and does not exhibit enantiomerism. Thus, the second statement is correct.

Glycylalanylglycine is a tripeptide formed by the condensation of three amino acids (glycine, alanine, and glycine). The number of peptide (amide) linkages in a peptide is equal to the number of amino acid residues minus one. Therefore, it has \(3 - 1 = 2\) amide linkages, not three. This makes the third statement incorrect.

The zwitterion of an amino acid contains both a basic carboxylate ion (\(-COO^-\)) and an acidic ammonium ion (\(-NH_3^+\)), allowing it to react with both acids and bases. Hence, it exhibits amphoteric behaviour, making the fourth statement correct.

Answer: Glycylalanylglycine has three amide linkages