Figure 1. The functions of mycothiol.

Mycothiol (MSH) is oxidised by reactive oxygen species (ROS) to mycothiol disulfide (MSSM). MSSM is reduced into MSH by the mycothiol disulfide reductase Mtr. MSH-dependent peroxidases, such as MPx, MsrA, and AhpE function in ROS detoxification. Electrophiles (RX) are conjugated to MSH to form MS-electrophiles (MSR), which are cleaved by the MSH S-conjugate amidase Mca to mercapturic acids (AcCysR) and exported from the cell. MSH serves as a cofactor for the alcohol dehydrogenase MscR and formaldehyde dehydrogenase AdhE for detoxification of NO and formaldehyde. Arsenate reductases CgArsC1/CgArsC2 conjugate MSH and arsenate As (V) to form As (V)-SM that is reduced to As (III) by mycoredoxin 1 (Mrx1). Metabolic reactions are catalyzed by enzymes such as maleylpyruvate isomerase requiring mycothiol as a cofactor for growth on diverse carbon sources. Under stress conditions, proteins are oxidised to mixed disulfides with MSH to form S-mycothiolated proteins that is reversed by the Mrx1/Mtr/MSH pathway.