grx5 is a mitochondrial glutaredoxin required for the activity of ironsulfur enzymes yeast cells contain a family of three monothiol glutaredoxins grx3 4 and 5 absence of grx5 leads to constitutive oxidative damage exacerbating that caused by external oxidants phenotypic defects associated with the absence of grx5 are suppressed by overexpression of ssq1 and isa2 two genes involved in the synthesis and assembly of ironsulfur clusters into proteins grx5 localizes at the mitochondrial matrix like other proteins involved in the synthesis of these clusters and the mature form lacks the first 29 amino acids of the translation product absence of grx5 causes 1 iron accumulation in the cell which in turn could promote oxidative damage and 2 inactivation of enzymes requiring ironsulfur clusters for their activity reduction of iron levels in grx5 null mutants does not restore the activity of ironsulfur enzymes and cell growth defects are not suppressed in anaerobiosis or in the presence of disulfide reductants hence grx5 forms part of the mitochondrial machinery involved in the synthesis and assembly of ironsulfur centers