Structural and Electron Paramagnetic Resonance (EPR) Studies of Mononuclear Molybdenum Enzymes from Sulfate-Reducing Bacteria

Carlos D. Brondino received his B.S. and Ph.D. degrees from the Universidad Nacional del Litoral (Argentina). He was a postdoctoral and research fellow at the Universidade Nova de Lisboa. He is now a professor and research fellow of CONICET in the Department of Physics of Facultad de Bioquímica y Ciencias Biológicas at the Universidad Nacional del Litoral.

Maria G. Rivas received her B.S. degree from the Universidad Nacional del Litoral (Argentina). She is now a Ph.D. student at the Universidade Nova de Lisboa.

Maria J. Romão received her Ph.D. degree from the Universidade Técnica de Lisboa, and she is now associate professor in the chemistry department of the Universidade Nova de Lisboa, where she is responsible for the group of protein crystallography (http://xtal.dq.fct.unl.pt/).

José J. G. Moura received his Ph.D. degree from the Universidade Nova de Lisboa, and he is now professor of chemistry in the chemistry department of the Universidade Nova de Lisboa, where he is responsible for the group of bioinorganic chemistry and protein engineering.

Isabel Moura received her Ph.D. degree from the Universidade Nova de Lisboa, and she is now professor of biochemistry in the chemistry department of the Universidade Nova de Lisboa, where she is responsible for the group of biophysical chemistry of proteins.

Molybdenum and tungsten are found in biological systems in a mononuclear form in the active site of a diverse group of enzymes that generally catalyze oxygen-atom-transfer reactions. The metal atom (Mo or W) is coordinated to one or two pyranopterin molecules and to a variable number of ligands such as oxygen (oxo, hydroxo, water, serine, aspartic acid), sulfur (cysteines), and selenium (selenocysteines) atoms. In addition, these proteins contain redox cofactors such as iron−sulfur clusters and heme groups. All of these metal cofactors are along an electron-transfer pathway that mediates the electron exchange between substrate and an external electron acceptor (for oxidative reactions) or donor (for reductive reactions). We describe in this Account a combination of structural and electronic paramagnetic resonance studies that were used to reveal distinct aspects of these enzymes.