Spectrophotometric assay for serum glutathione transferase: A re-examination

ObjectivesThe aim of the present paper is a careful re-examination of an automated spectrophotometric procedure for glutathione transferase (GST) activity in human serum described previously and used in many laboratories.Design and methodsGST activity in human serum has been assayed spectrophotometrically under various experimental conditions. Recombinant human GSTs and specific inhibitors were also used to check the possible occurrence of artifacts.ResultsBasal level of the enzyme calculated using this method turns out to be much higher than that found using RIA and ELISA procedures. Relevant pH-dependent artifacts deeply affect this spectrophotometric assay. Notably, spectral changes previously interpreted as a measure of basal activity, are mainly due to an increase of the spontaneous reaction between the two substrates.ConclusionGST activity in normal serum cannot be correctly determined with the spectrophotometric assay described previously because of the very low enzyme concentration and the pH-dependent artifacts.

► This is a re-examination of a published procedure for GST activity in human serum.
► Spectral changes previously interpreted as basal GST activity are mainly artifacts.
► GST in normal serum cannot be correctly determined by standard photometric assay.