close up of AlkB active site (IMAGE) DOE/Brookhaven National Laboratory Caption Active site: These closeups of the AlkB active site show how nine histidine amino acids (denoted as "H" in the left image) form a cavity (gray shaded region, right). This cavity guides the substrate (magenta) to the active site (near the two iron, Fe, atoms) in a single orientation, where only the terminal carbon-hydrogen bond can be cleaved. Modifying the enzyme to change the shape of this cavity could allow the enzyme to attack different C-H bonds. Credit Brookhaven National Laboratory Usage Restrictions OK for use with stories about this research License Original 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.