Mycothiol (AcCys-GlcN-Ins, MSH) is the major thiol-redox buffer in Actinomycetes, including Mycobacterium and Corynebacterium species. ). Protein S-mycothiolation controls the activities of several redox enzymes that function in detoxification of ROS and methionine sulfoxides, including the thiol peroxidase Tpx, the mycothiol peroxidase Mpx and the methionine sulfoxide reductase MsrA. Here we investigated the level of protein S-mycothiolation in Mycobacterium smegmatis under oxidative stress as well as its NaOCl stress response.