Catalyzes the conversion of methylglyoxal (MG) to D-lactate in a single glutathione (GSH)-independent step (PubMed:24758716). May play a role in detoxifying endogenously produced glyoxals. Involved in protection against reactive oxygen species (ROS) (By similarity). H2O + methylglyoxal = (R)-lactate + H(+) kcat is 58.0 min(-1) with methylglyoxal as substrate. Belongs to the peptidase C56 family. HSP31-like subfamily.