Serine hydrolase which catalyzes the hydrolysis of S-formylglutathione to glutathione and formic acid (Probable). Also hydrolyzes S-acetylglutathione and a range of carboxyesters in vitro (PubMed:11888210). Involved in the detoxification of formaldehyde (PubMed:16626737). H2O + S-formylglutathione = formate + glutathione + H(+) Activity toward p-nitrophenyl acetate inhibited by N-ethylmaleimide, 10-(fluoroethoxyphosphinyl)-N-(biotinamidopentyl)decanamide (FP-biotin), iodoacetamide, CuCl(2) and ZnSO(4), but not by phenylmethylsulfonyl fluoride, EDTA, Mg(2+), Mn(2+), Ca(2+) or paraoxon, an organo-phosphate inhibitor of serine hydrolases. Optimum pH is 7.6-8 for carboxyesterase activity. Fully active up to 55 degrees Celsius. Homodimer. The conserved Cys-59, implicated in catalysis in cysteine hydrolases, lies in close proximity to the serine hydrolase triad, serving a gate-keeping function in regulating access to the active site via disulfide formation with glutathione. Belongs to the esterase D family. Was originally classified as an esterase D due to its apparent insensitivity to serine hydrolase inhibitors. Truncated N-terminus.