The pyridoxal/2H2O exchange reaction of the α-CH of amino acids is known to be accompanied by racemisation: Thus by using a D-amino acid as the starting material any L-amino acid formed in the reaction will be essentially fully deuterated at its α-position. We have used this method to prepare α-deuterated L-valine and incorporated this biosynthetically into L. casei dihydrofolate reductase. A comparison of the αCH-NH fingerprint regions of COSY spectra of deuterated and normal DHFR complexes allows one to identify cross-peaks from 15 of the 16 valine residues.
