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. Involved in protection against reactive oxygen species (ROS) (By similarity). Important for viability in stationary phase. May negatively regulate TORC1 in response to nutrient limitation (PubMed:24706893). H2O + methylglyoxal = (R)-lactate + H(+) Homodimer. Present in processing bodies (P-bodies) and stress granule (SG) foci upon glucose starvation and heat shock. Induced during entry into stationary phase. Results in higher sensitivity to oxidative stress, reduced thermotolerance, accumulation of higher levels of reactive oxygen species, and reduced chronological life span. Belongs to the peptidase C56 family. HSP31-like subfamily.