Mediates cleavage of dimethylsulfonioproprionate (DMSP) into dimethyl sulfide (DMS) and acrylate. DMS is the principal form by which sulfur is transported from oceans to the atmosphere and is a key component of the ocean sulfur cycle. S,S-dimethyl-beta-propiothetin = acrylate + dimethyl sulfide + H(+) Homotetramer. Belongs to the aspartate/glutamate racemases family. ALMA1 subfamily.