Jasco 1500 Spectropolarimeter
The Jasco 1500 Spectropolarimeter (circular dichroism instrument) is housed in Dr. Ellen W. Moomaw’s Lab. All questions, training & scheduling inquiries, should be coordinated with her.
Circular dichroism (CD) is well known as a powerful probe of molecular conformations. It is a manifestation of the optical activity of chiral chromophores. CD can be used to measure the optical properties of small molecules. Another good use of CD in biochemistry is the estimation of secondary structure in proteins. This is possible because the CD of the peptide bond region absorbance is highly sensitive to the Ramachandran angles of amino acid residues, allowing clean discrimination between well-defined structural features such as alpha helices and beta strands, which have different and well defined Ramachandran stability valleys. This is not the case for conformations lumped together as ‘random coil.’ Hence CD as a measure of secondary structure is typically descriptive rather than quantitatively accurate, although reasonable estimates of alpha helical and beta sheet content can be made.
Circular dichroism is a very powerful probe of changes in protein conformation. For example, it is possible to observe small changes in helix content using difference methods, and effects of mutation and protein-protein interactions can be studied. These measurements are relatively easy to carry out and produce reliable, easily interpreted results. Studies of protein conformation rely on the absorbance of the chiral peptide bond region and are the result of electric and magnetic coupling of light to transitions.