GLUTATHIONE S-TRANSFERASES: A BRIEF ON CLASSIFICATION AND GSTM1-T1 ACTIVITY

The glutathione S-transferase (GST) isoenzyme superfamilies detoxify a wide-range of toxic chemicals and environmental substances are extensively expressed in mammalian tissues. Liver and pancreas are the sites where cytosolic Phase I and phase II biotransformation GSTs enzymes have characteristic expression. GSTs play a key role in the deactivation of reactive oxygen species (ROS) and the metabolism of lipids, chemotherapeutic agents. GSTs are mainly involved in conjugation of reduced glutathione (GSH) with diverse substrates specificity and it is possible that genetic variations in these enzymes will influence cellular response to the environmental agents. GSTs are overexpressed in response to a chemical or oxidative stress as an adaptive physiology and upregulated in cancerous state of organ or tissue. GSTs are essentially involved in susceptibility to various forms of cancer as they are vital in detoxification mechanism to metabolize the environmental carcinogens. GSTM1 encodes for a class mu GST isoenzyme involved in polycyclic aromatic hydrocarbons (PAHs) detoxification. The substrates of GSTM1 include benzo(a)pyrene, benzo(c)phenanthrene, benzo(g)chrysene and other carcinogens. They can catalyze in-vitro GSH conjugation with several potent carcinogenic epoxides including aflatoxin B1(AFB1)8,9-epoxide and electrophilic metabolites of PAHs present in tobacco smoke. Ethylene dibromide, p-nitrobenzyl chloride, p-nitrophenetyl bromide, methyl chloride, and methyl iodide, are known substrates for GSTT1 or GST Theta (θ). GST Theta is most primitive among other known GSTs and widely expressed in nature.