Enzymatic synthesis of some 15N-labelled l-amino acids

Our group has developed a stereospecific enzymatic method, which is very efficient for the in vitro synthesis of l-¹⁵N]serine, l-¹⁵N]methionine and l-¹⁵N]glutamic acid. These amino acids were prepared from the corresponding α -ketoacids in the suitable enzymatic systems. The bacterial NAD-dependent amino acid dehydrogenases alanin dehydrogenase, leucin dehydrogenase and glutamate dehydrogenase were used as catalysts. Glucose dehydrogenase was used for the regeneration of NADH and ¹⁵NH₄Cl as isotopically labelled material at 99 at.% ¹⁵N. All reactions are inexpensive and easy to perform on a synthetically useful scale (1-10g) giving high yields of l-amino acids. The ¹⁵N isotope content was determined by mass spectrometry.