@P04898-1@ in which non-@H02714@ iron is coordinated with cysteine sulfur and usually also with inorganic sulfur. Divided into three major categories: rubredoxins; 'simple iron-sulfur @P04898-2@', containing only @IT06779@; and 'complex iron-sulfur @P04898-2@', containing additional active redox centres such as @F02423@, molybdenum or @H02714@. In most iron-sulfur @P04898-2@, the clusters function as electron-transfer groups, but in others they have other functions, such as @C00874@ of hydratase/dehydratase reactions, maintenance of protein structure, or regulation of activity.