Reactivation of oxidized AtSS1: protein was first oxidized by CuCl2, and then it was desalted and treated with water, reduced Trxs and DTTred. Trxs (100 μM) were reduced with 0.5 mM DTTred. Deactivation of reduced AtSS1: protein was first reduced by DTTred, and then it was desalted and treated with water, oxidized Trxs and CuCl2. Trxs (150 μM) were oxidized with 300 μM CuCl2. Fully reduced sample was set as 100%. Desalting control (sample treated identically to oxidized Trxs but Trxs were omitted) was used to test that CuCl2 left after desalting is not the major deactivating factor. Activity was assayed by SCGA using maltotriose as acceptor; results are the mean of two technical replicates (±SD).