Question

Which peptide has greater absorbance at 280 nm?

A. Gln–Leu–Glu–Phe–Thr–Leu–Asp–Gly–Tyr

B. Ser–Val–Trp–Asp–Phe–Gly–Tyr–Trp–Ala

Short answer

Peptide B has greater absorbance because it has tryptophan and other aromatic residues.

Step-by-step solution

Tryptophan has greatest absorbance

Tryptophan has the greatest absorbance at 280nm because of its higher resonance energy transfer. Also, the fluorescence spectrum of aromatic residues such as tyrosine and phenylalanine resembles that of tryptophan.

Peptide B had greater absorbance

Peptide A has Gln–Leu–Glu–Phe–Thr–Leu–Asp–Gly–Tyr sequence. In this amino acid sequence, there is absence of tryptophan amino acids which has the highest absorbance. However, peptide B has Ser–Val–Trp–Asp–Phe–Gly–Tyr–Trp–Ala sequence. In this amino acid sequence, there is presence of tryptophan amino acids which has the highest absorbance due to its greater absorptivity.

Hence, peptide B has greater absorbance.