A Disintegrin and Metalloprotease 17 (ADAM17) can cause the fast release of growth factors and inflammatory mediators from the cell surface. Its activity has to be turned on which occurs by various stimuli. The active form can be inactivated by a structural change in its ectodomain, related to the pattern of the formed disulphide bridges. The switch-off is executed by protein disulfide isomerases (PDIs) that catalyze an isomerization of two disulfide bridges and thereby cause a disulfide switch. We demonstrate that the integrity of the CGHC-motif within the active site of PDIs is indispensable. In particular, no major variation is apparent in the activities of the two catalytic domains of PDIA6. The affinities between PDIA1, PDIA3, PDIA6 and the targeted domain of ADAM17 are all in the nanomolar range and display no significant differences. The redundancy between PDIs and their disulfide switch activity in ectodomains of transmembrane proteins found in vitro appears to be a basic characteristic. However, different PDIs might be required in vivo for disulfide switches in different tissues and under different cellular and physiological situations.