On the Way to a Biological Alternative (IMAGE) University of Freiburg Caption The catalytic center of vanadium nitrogenase: an iron-vanadium cofactor with an unusual carbonate ligand. Credit Graphic: Oliver Einsle Usage Restrictions The image may only be used with appropriate caption or credit. 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.