Catalyzes the synthesis of D-serine from L-serine. D-serine is a key coagonist with glutamate at NMDA receptors. Has dehydratase activity towards both L-serine and D-serine. L-serine = D-serine D-serine = NH4(+) + pyruvate L-serine = NH4(+) + pyruvate Allosterically activated by magnesium, and possibly also other divalent metal cations. Allosterically activated by ATP, ADP or GTP (By similarity). Competitively inhibited by malonate. Homodimer. S-nitrosylated, leading to decrease the enzyme activity. Belongs to the serine/threonine dehydratase family.