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 beta-carbon of alanine (beta-halo-alanines and L-serine-O-sulfate), which can act as enzyme-activated inhibitors, and compounds containing beta-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.

A short, versatile chemical synthesis of l- and d-amino acids stereoselectively labelled solely in the beta position

L- and D-Amino acids which are stereoselectively labelled solely either in the 3-pro-R or in the 3-pro-S-positions have been prepared by a relatively short chemical synthesis in ee of 81 to 86%. This involves Sharpless' aminohydroxylation and cyclisation with inversion of stereochemistry at C-2 to give the stereoselectively labelled D- and L-aziridines and 10a and 10b, and 8a and 8b. These have previously been modified and cleaved with inversion of stereochemistry at C-3 using a number of nucleophiles to give a large variety of protected amino acids. Synthesis of the labelled D- and L-beta-chloroalanines 22a and 22b and 25a and 25b is described here.