Evidence for a glycoconjugate form of glutathione S-transferase pI

The anionic form of glutathione S-transferase from human (GST pi) and rat (GST Yp) sources has been shown to exist in multiple forms which have similar molecular weights but different isoelectric points (pIs). Treatment with endoglycosidase H caused the acidic forms of GST Yp to be converted to proteins with more basic pIs as compared to the untreated control mixtures, suggesting that an N-linked mannose moiety containing acidic residues had been removed. Inability to detect these carbohydrates by techniques requiring unsubstituted vicinal hydroxyls further suggested acidic substitutions on the sugar moiety. GST pi/Yp carbohydrate modifications were also identified by differential staining procedures. These data represent the first indication that glycosylation of GST can occur. Additionally, this may offer an explanation for the often seen microheterogeneity within a class of GST isozymes.