Why Are Nodules Red? (image) Washington University in St. Louis Caption An iron-containing protein not unlike the hemoglobin in our red blood cells colors root nodules. Called leghemoglobin (leg- for "legume") it ferries oxygen to the respiring bacteria, just as hemoglobin ferries oxygen to our respiring cells. But leghemoglobin holds oxygen much more tightly than hemoglobin and dispenses it more stingily because oxygen can poison the bacterial enzyme that fixes nitrogen. Credit Hari Krisnan 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.