title: Cofactors of serine racemase that physiologically stimulate the synthesis of the N-methyl-D-aspartate (NMDA) receptor coagonist D-serine.
abstract: High levels of d-serine occur in the brain, challenging the notion that d-amino acids would not be present or play a role in mammals. d-serine levels in the brain are even higher than many l-amino acids, such as asparagine, valine, isoleucine, and tryptophan, among others. d-serine is synthesized by a serine racemase (SR) enzyme, which directly converts l- to d-serine. We now report that SR is a bifunctional enzyme, producing both d-serine and pyruvate in cultured cells and in vitro. Transfection of SR into HEK 293 cells elicits synthesis of d-serine and augmented release of pyruvate to culture media. We identified substances present in HEK 293 and astrocyte cell extracts that strongly stimulate d-serine production by SR and elicit production of pyruvate. Experiments with recombinant enzyme reveal that Mg(2+) and ATP present in the cell extracts are physiological cofactors and increase 5- to 10-fold the rates of racemization and production of pyruvate. As much as three molecules of pyruvate are synthesized for each molecule of d-serine produced by SR. This finding constitutes a previously undescribed mechanism underlying d-amino acid synthesis in mammals, different from classical amino acid racemases present in bacteria. Our data link the production of d-serine to the energy metabolism, with implications for the metabolic and transmitter crosstalk between glia and neurons.
authors.affiliation: Department of Biochemistry, Federal University of Rio de Janeiro, Rio de Janeiro RJ 21941-590, Brazil.
authors.forename: Joari
authors.initials: J
authors.lastname: De Miranda
authors.forename: Rogerio
authors.initials: R
authors.lastname: Panizzutti
authors.forename: Veronika N
authors.initials: VN
authors.lastname: Foltyn
authors.forename: Herman
authors.initials: H
authors.lastname: Wolosker
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D006801:Humans; D008024:Ligands; D008274:Magnesium / Q000378:metabolism*; D051379:Mice; D019289:Pyruvic Acid / Q000378:metabolism; D019998:Racemases and Epimerases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists*; D012694:Serine / Q000096:biosynthesis*; D000099300:Serine Racemase
chemical_list: D000244:Adenosine Diphosphate; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D008024:Ligands; D008274:Magnesium; D019289:Pyruvic Acid; D019998:Racemases and Epimerases; D016194:Receptors, N-Methyl-D-Aspartate; D012694:Serine; D000099300:Serine Racemase