SRR, also known as serine racemase, is an enzyme which generates D-serine from L-serine. D-serine acts as a neuronal signaling molecule by activating NMDA receptors in the brain. Mammalian serine racemase is a pyridoxal 5'-phosphate dependent enzyme that catalyzes both the racemization of L-serine to D-serine and also the elimination of water from L-serine, generating pyruvate and ammonia. The enzyme is physiologically stimulated by divalent cations (e.g., magnesium) and is allosterically activated by the magnesium/ATP complex. Recombinant human SRR protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography.