Chapter 27: Amino Acids, Peptides and Proteins

Disulfide Bonds

• Thiols readily react with each other to form disulfides (review ?)
• In proteins, the amino acid cysteine contains a thiol group and readily forms disulfides so linking two cysteine units together.
• This simple linkage has important consequences for protein shape as this covalent interaction restricts the conformations.
• Disulfides can be either intramolecular or intermolecular (see image on the right below)

Two cysteine units form a simple disulfide

A schematic diagram of two disulfides from the protein structure of bovine insulin.

The following 3D JMOL image shows the A and B chains of human insulin and contains 3 disulfide linkages including those described above
(bovine and human insulin differ only by 3 amino acid residues in these two chains)
 

© Dr. Ian Hunt, Department of Chemistry, University of Calgary