In order to gather biochemical information about class III glutaredoxins (CCxC/S active sites), the active sites of two poplar class I glutaredoxins, GrxC1 and C4, CGYC and CPYC, respectively, were transformed into CCMC or CCMS. All the recombinant mutated proteins bind [2Fe-2S] centers into holodimers, whereas monomeric apoforms possess glutathione-dependent reductase activity. The functionally important, hydrophobic GALWL C-terminal end, found in most class III glutaredoxins, prevents expression in Escherichia coil. Changing the C-terminal end of GrxS7.2, a genuine class Ill glutaredoxin, allowed purifying some holoproteins. These properties are discussed considering the documented function of class III glutaredoxins in development. (C) 2010 Elsevier Inc. All rights reserved.