In studies involving model tetrapeptides, to which atom is 7-amino-4-methylcoumarin (AMC) covalently attached?

• A. The amino nitrogen of the N-terminal amino acid
• B. The carboxyl oxygen of the C-terminal amino acid
• C. The carboxyl carbon of the C-terminal amino acid
• D. The alpha carbon of the N-terminal amino acid

Answer: (B)

Verified step by step guidance

1. Understand the structure of a tetrapeptide: A tetrapeptide consists of four amino acids linked by peptide bonds. Each amino acid has an amino group (-NH2), a carboxyl group (-COOH), and a side chain (R group). The N-terminal amino acid is the one with a free amino group, and the C-terminal amino acid is the one with a free carboxyl group.
2. Learn about 7-amino-4-methylcoumarin (AMC): AMC is a fluorescent molecule often used in biochemical studies. It is typically covalently attached to peptides or proteins to enable detection or measurement of enzymatic activity.
3. Determine the attachment site: AMC is commonly attached to the carboxyl group of the C-terminal amino acid in peptides. This is because the carboxyl group (-COOH) can form a covalent bond with AMC through a chemical reaction, such as esterification or amidation.
4. Eliminate incorrect options: The amino nitrogen of the N-terminal amino acid is not typically involved in AMC attachment. Similarly, the alpha carbon of the N-terminal amino acid is not chemically reactive in this context. The carboxyl oxygen of the C-terminal amino acid is part of the carboxyl group, but the bond is formed with the carboxyl carbon.
5. Conclude the correct answer: The carboxyl carbon of the C-terminal amino acid is the atom to which AMC is covalently attached. This allows AMC to be linked to the peptide for experimental purposes.