Iron-sulfur clusters: Formation, perturbation, and physiological functions

Iron-sulfur proteins occur in all life forms. Ferredoxins and Rieske proteins each contain a (2Fe-2S) cluster whereas photosystem I(PSI) contains three (4Fe-4S) clusters. Essential enzymes such as sulfite reductase, nitrite reductase, nitrogenase, glutamate synthase, aconitase, succinate dehydrogenase, ferredoxin/thioredoxin reductase, as well as many other vital proteins, each contain a (4Fe-4S) cluster. iron-sulfur clusters are formed enzymatically from cysteinyl-sulfur and ferritin-sequestered iron. Many iron-sulfur clusters are inactivated by O-2 and/or reactive oxygen species (ROS) such as O-2(.-). Perhaps 0.1% of the electrons passing through either the mitochondrial electron transport chain or PSI result in the formation of O2(.-). Many plant stresses increase ROS formation, which subsequently may perturb iron-sulfur clusters. Plants have evolved th;ee different superoxide dismutases (SODs) to control the internal concentrations of harmful ROS. Possible roles of functional and non-functional iron-sulfur clusters in the coordination of metabolic activities of stressed and non-stressed plants are discussed. (C) Elsevier, Paris.