The Jasco J-815 circular dichroism (CD) spectroscopy measures differences in the absorption of left-handed polarized light versus right-handed polarized light that arise due to structural asymmetry. The absence of regular structure results in zero CD intensity, while an ordered structure results in a spectrum which can contain both positive and negative signals.

CD can be used for: 

• Determination if a protein is folded
• Characterization of  secondary structure (α-helix, β-sheet)
• Detection of changes in structure upon mutagenesis
• Studying conformational stability of proteins:
  • pH stability
  • denaturant stability (urea, guadinium hydrochloride) 
  • temperature
  • buffers
  • addition of stabilizers
• Detection of Changes in the conformation of a protein upon protein:protein interaction

Characterization of secondary structure is probably the most used CD spectroscopy application. Secondary structure can be identified in the "far-UV" spectral region (190-250 nm). The protein peptide bond is the chromophore, and it is possible to detect a signal if the protein is in a specific secondary structural conformation (α-helix, β-sheet).