Regulation of serine racemase activity by amino acids

The effects of various amino acids on the activity of serine racemase, purified from mouse brain, were examined. Those acting as inhibitors included compounds with electron withdrawing groups on the β-carbon of alanine (β-halo-alanines and l-serine-O-sulfate), which can act as enzyme-activated inhibitors, and compounds containing β-SH groups (cysteine and homocysteine) which react with enzyme-bound pyridoxal phosphate to form thiazolidine derivatives. Glycine and a series of metabolites related to l-aspartic acid (l-aspartic acid, l-asparagine, and oxaloacetic acid) were also found to be competitive inhibitors of the racemase. The Ki values for glycine and aspartic acid inhibition were 0.15 and 1.9 mM, respectively, indicating that alterations in the concentrations of these amino acids might play a role in the regulation of d-serine synthesis.