Purification of serine racemase: biosynthesis of the neuromodulator D-serine.
High levels of D-serine occur in mammalian brain, where it appears to be an endogenous ligand of the glycine site of N-methyl-D-aspartate receptors. In glial cultures of rat cerebral cortex, D-serine is enriched in type II astrocytes and is released upon stimulation with agonists of non-N-methyl-D-aspartate glutamate receptors. The high levels of D-serine in discrete areas of rat brain imply the existence of a biosynthetic pathway. We have purified from rat brain a soluble enzyme that catalyzes the direct racemization of L-serine to D-serine. Purified serine racemase has a molecular mass of 37 kDa and requires pyridoxal 5'-phosphate for its activity. The enzyme is highly selective toward L-serine, failing to racemize any other amino acid tested. Properties such as pH optimum, Km values, and the requirement for pyridoxal phosphate resemble those of bacterial racemases, suggesting that the biosynthetic pathway for D-amino acids is conserved from bacteria to mammalian brain.
Wolosker
H
H
The Johns Hopkins University, School of Medicine, Departments of Neuroscience, Pharmacology and Molecular Sciences, and Psychiatry, 725 North Wolfe Street, Baltimore, MD 21205, USA.
Sheth
K N
KN
Takahashi
M
M
Mothet
J P
JP
Brady
R O
RO
Ferris
C D
CD
Snyder
S H
SH
D000591:Amino Acid Isomerases / Q000302:isolation & purification*; D000625:Aminooxyacetic Acid / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009457:Neuroglia; D011732:Pyridoxal Phosphate / Q000378:metabolism; D019998:Racemases and Epimerases / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists; D012694:Serine / Q000096:biosynthesis*; D013053:Spectrophotometry; D013379:Substrate Specificity; D013696:Temperature
D004791:Enzyme Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; D000625:Aminooxyacetic Acid; D012694:Serine; D011732:Pyridoxal Phosphate; D019998:Racemases and Epimerases; D000591:Amino Acid Isomerases