Catalyzes the conversion of methylglyoxal (MG) to D-lactate in a single glutathione (GSH)-independent step. May play a role in detoxifying endogenously produced glyoxals (PubMed:24302734). Involved in protection against reactive oxygen species (ROS) (PubMed:17395014). Important for viability in stationary phase. May negatively regulate TORC1 in response to nutrient limitation (PubMed:24706893). H2O + methylglyoxal = (R)-lactate + H(+) kcat is 75.0 min(-1) with methylglyoxal as substrate. Homodimer. Present in processing bodies (P-bodies) and stress granule (SG) foci upon glucose starvation and heat shock. Up-regulated 10- to 30-fold during entry into stationary phase, by hydrogen peroxide or diamide stress, by heat stress, and by growth in the presence of the proline analog azetidine-2-carboxylic acid. Cys-138 is easily oxidized to sulfinic acid. Results in higher sensitivity to oxidative stress, reduced thermotolerance, accumulation of higher levels of reactive oxygen species, and reduced chronological life span. No protease activity could be detected. Present with 358 molecules/cell in log phase SD medium. Belongs to the peptidase C56 family. HSP31-like subfamily.