Which amino acid residues in hemoglobin are primarily carbamylated at low pH?

• A. N-terminal amino groups of the globin chains
• B. Side chains of aspartate residues
• C. C-terminal carboxyl groups of the globin chains
• D. Side chains of lysine residues

Answer: (A)

Verified step by step guidance

1. Understand the concept of carbamylation: Carbamylation is a chemical reaction where a carbamoyl group (-CONH2) is added to amino groups. This process is influenced by pH, as low pH can protonate amino groups, making them less reactive.
2. Identify the functional groups in hemoglobin that can undergo carbamylation: Hemoglobin contains N-terminal amino groups, side chains of lysine residues, side chains of aspartate residues, and C-terminal carboxyl groups. Each of these groups has distinct chemical properties.
3. Analyze the reactivity of N-terminal amino groups: At low pH, the N-terminal amino groups are protonated, reducing their nucleophilicity and making them less likely to be carbamylated.
4. Evaluate the side chains of lysine residues: Lysine contains an ε-amino group in its side chain, which remains nucleophilic even at low pH, making it a primary target for carbamylation.
5. Consider the side chains of aspartate residues and C-terminal carboxyl groups: Both aspartate side chains and C-terminal carboxyl groups are negatively charged at physiological pH but become protonated at low pH, reducing their reactivity and likelihood of carbamylation.