Occurrence of D-serine in rice and characterization of rice serine racemase

Germinated, unpolished rice (Oryza sativa L.) was found to contain a substantial amount of D-serine, and the ratio of the D-enantiomer to the L-enantiomer was higher for serine than for other amino acids. A serine racemase (E.C.5.1.1.18) was characterized from the source, whose structure was distorted by addition of Mg2+; this structural change probably regulates competing racemase and dehydratase activities.