Heme Crossroads (IMAGE) DOE/Pacific Northwest National Laboratory Caption Numbered heme groups (in color) lie within MtrF protein's framework (in gray) and shuttle electrons from one end of the protein to the other. Credit Cortland Johnson (PNNL) and Julian Breuer Usage Restrictions Please credit Johnson/Breuer/PNNL 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.