A mycothiol (MSH, N-acetyl-cysteinyl-glucosaminyl-inositol) S-conjugate amidase, it recycles conjugated MSH to the N-acetyl cysteine conjugate and the MSH precursor. Involved in MSH-dependent detoxification of a number of alkylating agents and antibiotics. Activity is specific for the mycothiol moiety. H2O + mycothiol S-conjugate = 1D-myo-inositol 2-amino-2-deoxy-alpha-D-glucopyranoside + an N-acetyl-L-cysteine-S-conjugate Binds 1 zinc ion per subunit. Partially inhibited by MSH when MSmB (a bimane derivative of MSH) is used as substrate. at 25 mM HEPES, pH 7.5, 30 degrees Celsius. Optimum pH is 7-9. Monomer. Loss of amidase activity on MSmB, no production of the mercapturic acid product AcCys-mB. Limited degradation of MS-RifSV, a rifamycin S MSH conjugate. Increased sensitivity to streptomycin, slight increase in sensitivity to rifamycin but no other antibiotics tested. Increased sensitivity to iodoacetamide, N-ethylmalemide (NEM) and redox cycling (oxidant) agents known to conjugate with MSH such as menadione and plumbagin, but not other oxidants. Belongs to the MshB deacetylase family. Mca subfamily.