Copper Binding to Enzyme (IMAGE) University of California - Berkeley Caption The crystal structure of the cAMP-degrading enzyme phosphodiesterase PDE3B, showing two magnesium atoms (green) in the active site. Copper binds one of the amino acid residues in the pink loop at the left, blocking the activity of the enzyme. Credit Lakshmipriya Krishnamoorthy and Joseph Cotruvo Jr., UC Berkeley Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.