Analysis of Characteristic Peaks of Lysine in Circular Dichroism Spectroscopy

Circular Dichroism (CD) is a technique for studying the secondary and tertiary structures of proteins, nucleic acids, and other biological macromolecules. By measuring the optical rotation of molecules at specific wavelengths, information about their structure can be obtained.

 

The optical rotation of lysine (Lys) is mainly present in the circular dichroism in the far ultraviolet region. The characteristic peaks of a single lysine or simple lysine peptide segment mainly appear in the far ultraviolet region (about 190-240 nm). The main CD signal of lysine in this region comes from the ε-amino group of its side chain, and these signals are often mixed with the CD signals produced by the backbone structure of the protein. Therefore, for large protein structures, the optical rotation signal of the lysine residue may be obscured by the background protein structure signal.

 

The CD characteristic peaks of proteins are mainly determined by their secondary structures (such as α-helices, β-sheets, random coils, etc.). For the secondary structure of proteins, here are some common CD characteristic peaks:

 

1. α-Helix

There is a positive characteristic peak at about 190-195 nm and two negative characteristic peaks at 208 and 222 nm.

 

2. β-Sheet

There is a positive characteristic peak at about 195 nm and a negative characteristic peak at about 215-218 nm.

 

3. Random Coil

It is mainly characterized by a negative peak near 200 nm.

 

It should be noted that these wavelengths are only approximations, and the actual characteristic peak positions may vary depending on the specific sequence and conditions of the protein.