Hydrogen Exchange at the β‐Carbon of Amino Acids during Transamination

Abstract

The hydrogen exchange at the β-carbon of l-alanine, l-glutamate and l-aspartate with water has been examined during transamination catalyzed by glutamic-oxaloacetic transaminase and by glutamic-pyruvic transaminase. A significant hydrogen exchange at the β-carbon has been demonstrated during incubation of l-[3-³H]alanine + glutamic-pyruvic transaminase, l-[3-³H]alanine +α-oxo-glutarate + glutamic-pyruvic transaminase, l-[3-³H]glutamate + glutamic-oxaloacetic transaminase, l-[3-³H]glutamate + oxaloacetate + glutamic-oxaloacetic transaminase, and l-[3-³H]glutamate + pyruvate + glutamic-pyruvic transaminase as shown by the appearance of ³H₂O. No hydrogen exchange at the β-carbon of l-glutamate occurred during incubation of l-[3-³H]-glutamate with glutamic-pyruvic transaminase alone. The hydrogen exchange at the β-carbon of l-glutamate coincides with transamination as demonstrated by nuclear magnetic resonance studies of ²H₂O-l-glutamate exchange during transamination by glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase. No hydrogen exchange at the β-carbon occurred during transamination of l-aspartate by glutamic-oxaloacetic transaminase as shown by nuclear magnetic resonance spectroscopy and confirmed by The results are discussed with special reference to the different equilibria between the pyridoxal form and the pyridoxamine form of glutamic-oxaloacetic transaminase and of glutamic-pyruvic transaminase.