Mycothiol (MSH), a conjugate of glucosamine, cysteine and inositol, is the Actinobacteria equivalent of glutathione. It serves as a pool for both the unstable cysteine and reduction equivalents. Mycothiol takes part in enzymatic reactions including detoxification of electrophilic compounds, inactivation of reactive oxygen and nitrogen species, reductions, and isomerizations.
M. smegmatis mutants devoid of MSH are sensitive to oxidative and nitrosative stress, and antibiotics. In M. tuberculosis, however, mycothiol synthesis is essential, no null mutants are known. Results from MshD mutants, which have about 1 per cent of MSH, show the importance of mycothiol in environments where antimicrobial factors, including reactive oxygen and reactive nitrogen intermediates, are formed, such as within macrophages (Newton et al, 2008; Rawat and Av-Gay, 2007)