Assay of glutathione reductase in crude tissue homogenates using 5,5'-dithiobis(2-nitrobenzoic acid)

A method for assaying glutathione reductase (GSH; EC 1.6.4.2) in crude plant extracts is described. The method is based on the increase in absorbance at 412 nm when 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) is reduced by GSH. The effects of the following parameters on the assay were tested: various buffers, pH, buffer concentration, compounds commonly present in enzyme preparations, thiols, and the presence of another NADPH-dependent enzyme. The assay is more sensitive and less subject to interference than the widely used assay where NADPH oxidation is monitored. In particular, the specificity of DTNB allows assay of glutathione reductase in the presence of other NADPH-dependent enzymes and common protein extract contaminants.