Plasmodium Enzyme Phosphoethanolamine Methyltransferase (image) Washington University in St. Louis Caption A cartoon based on the electron density map makes it easier to see the protein's structure and figure out how it works. The enzyme's job is to add a methyl group -- three times -- to a starting molecule as part of a process for making cell membranes. In this cartoon, the phosphate is a stand-in for the starting molecule and the green molecule is the one that donates a methyl group. Both are positioned in the active site of the enzyme, the pocket where the chemistry takes place. Credit Joseph Jez Usage Restrictions please credit 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.