Localization and Characterization of Glutathione-s-transferase Isozymes Alpha, Mu, and Pi Within the Mouse Vomeronasal Organ

The nasal cavity of vertebrates contains a variety of xenobiotic metabolizing enzymes that possess a broad range of substrate specificity ranging from metabolism of drugs, carcinogens, and steroid hormones, to dietary components and environmental pollutants. This investigation sought to localize the cellular expression and distribution of glutathione-s-transferase (GST) alpha, mu, and pi detoxifying enzymes, and to study GST activity toward different substrates in the mouse vomeronasal organ (VNO). Immunohistochemistry was used to identify GST alpha, mu and pi in the non-sensory and sensory layer of the VNO. Western blot analysis of cytosolic proteins revealed a qualitatively higher enzyme expression of GST alpha and mu in the main olfactory tissue (OE) in comparison to VNO tissue, whereas the GST pi isozyme was equally expressed in both. Total GST metabolism of 1-chloro-2, 4-dinitrobenzene (CDNB) revealed a higher activity level in the OE when compared to the VNO. In contrast, thin-layer chromatographic analysis of GST conjugation of the odorant, trans-2-hexenal (t-hex) (10 mM) showed more conjugate formed per unit protein in the VNO than the OE. The analysis of GST expression and enzyme activity within the VNO parallels the reported localization of phase I metabolizing enzymes and suggests that GST isozymes play independent roles that characterize multiple processes within VNO chemosensitivity.