Catalyzes the synthesis of D-serine from L-serine (PubMed:19249065, PubMed:20564571). Has dehydratase activity towards both L-serine and D-serine (PubMed:19249065, PubMed:20564571). L-serine = D-serine L-serine = NH4(+) + pyruvate D-serine = NH4(+) + pyruvate Inhibited by semicarbazide, hydroxylamine, aminooxyacetate, sodium borate or phenylhydrazine (PubMed:19249065). Racemase activity is enhanced by Ca(2+), Mg(2+) and is decreased by ATP, Cu(2+), Zn(2+) (PubMed:19249065, PubMed:20564571). Hydratase activity is enhanced by ATP and is decreased by Ca(2+), Mg(2+), Co(2+), Cu(2+), Ni(2+), Zn(2+) (PubMed:19249065, PubMed:20564571). Optimum pH is 9.5 for racemization and 9.0 for hydration. Optimum temperature is 35 degrees Celsius (racemase or dehydratase activity). Homodimer. Belongs to the serine/threonine dehydratase family.