Involved in bacillithiol (BSH) biosynthesis. Catalyzes the second step of the pathway, the deacetylation of N-acetylglucosaminylmalate (GlcNAc-Mal) to glucosamine malate (GlcN-Mal). Could also be involved in bacillithiol-detoxifying pathways through formation of S-mercapturic adducts. (S)-malyl N-acetyl-alpha-D-glucosaminide + H2O = (S)-malyl alpha-D-glucosaminide + acetate kcat is 6.48 sec(-1) with GlcNAc-Mal. kcat is 0.031 with bacillithiol-S-bimane (BSmB). Belongs to the PIGL family.