Which amino acid contributes to the CD signal in the far UV region but not the near UV region of a fully folded protein?

Which amino acid contributes to the CD signal in the far UV region but not the near UV region of a fully folded protein?

• A. Tryptophan
• B. Phenylalanine
• C. Alanine
• D. Tyrosine

Answer: (C)

The amino acid that contributes to the circular dichroism (CD) signal in the far UV region but not in the near UV region of a fully folded protein is alanine. This stems from the nature of different amino acids and how their side chains interact with polarized light. In the far UV region (typically around 190-250 nm), the CD signals are primarily due to the peptide bonds (the backbone of the protein) and any side chain contributions that are able to rotate polarized light, specifically through the transition moments of the phi and psi angles present in the backbone structure. Alanine, being a simple amino acid with an aliphatic side chain, does not have any additional chromophores that contribute significantly to the signal in the near UV region, which typically involves aromatic side chains. On the other hand, tryptophan, phenylalanine, and tyrosine are all aromatic amino acids that possess significant electronic transitions in the near UV region (around 250-300 nm) due to their aromatic rings. These amino acids contribute to the near UV CD signal because they have distinct molecular structures that allow them to interact with light in ways that alanine does not. Thus, while alanine can contribute to the far UV signal

The amino acid that contributes to the circular dichroism (CD) signal in the far UV region but not in the near UV region of a fully folded protein is alanine. This stems from the nature of different amino acids and how their side chains interact with polarized light.

In the far UV region (typically around 190-250 nm), the CD signals are primarily due to the peptide bonds (the backbone of the protein) and any side chain contributions that are able to rotate polarized light, specifically through the transition moments of the phi and psi angles present in the backbone structure. Alanine, being a simple amino acid with an aliphatic side chain, does not have any additional chromophores that contribute significantly to the signal in the near UV region, which typically involves aromatic side chains.

On the other hand, tryptophan, phenylalanine, and tyrosine are all aromatic amino acids that possess significant electronic transitions in the near UV region (around 250-300 nm) due to their aromatic rings. These amino acids contribute to the near UV CD signal because they have distinct molecular structures that allow them to interact with light in ways that alanine does not.

Thus, while alanine can contribute to the far UV signal