2022 CNBO

A and C

To determine which short chain polypeptide has the greatest light absorption under 280 nm, we need to consider the properties of the amino acids present and their respective absorption spectra.

The absorption of light by a molecule depends on its electronic structure, which is influenced by the types of atoms and functional groups present. In the case of polypeptides, the absorption of ultraviolet (UV) light is primarily due to the presence of aromatic amino acids, such as phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr).

Let's analyze each option:

A. Glu-Ala-Phe-Gln:

This polypeptide contains phenylalanine (Phe), which is an aromatic amino acid. Aromatic compounds, including Phe, are known to absorb UV light. Therefore, this polypeptide has the potential to absorb light around 280 nm.

B. His-Thr-Asp:

None of the amino acids present in this polypeptide (histidine, threonine, aspartic acid) are aromatic amino acids. Therefore, this polypeptide is less likely to absorb light at 280 nm.

C. Ser-Pro-Trp-Gly:

This polypeptide contains tryptophan (Trp), which is an aromatic amino acid. As mentioned earlier, aromatic compounds, including Trp, have the potential to absorb UV light. Hence, this polypeptide has the potential to absorb light around 280 nm.

D. His-Lys-Arg-Gly:

None of the amino acids present in this polypeptide (histidine, lysine, arginine) are aromatic amino acids. Therefore, this polypeptide is less likely to absorb light at 280 nm.

Comparing the options, both options A and C contain an aromatic amino acid (Phe and Trp, respectively), which gives them the potential for light absorption around 280 nm. Therefore, the correct answer is A and C.