Glutathione S-transferase mu 3, also known as GSTM3, is member of the glutathione s-transferase (GST) family of proteins. There are eight families of GST proteins, namely alpha, kappa, mu, omega, pi, sigma, theta and zeta, each of which is composed of proteins that have a variety of functions throughout the cell. The mu class of enzymes functions in the detoxification of electrophilic compounds, including carcinogens, therapeutic drugs, environmental toxins and products of oxidative stress, by conjugation with glutathione.