Enzymatic preparation of α- and β-deuterated or tritiated amino acids with l-methionine γ-lyase

Abstract

l-Methionine γ-lyase catalyzes the exchange of α- and β-hydrogens of l-methionine and S-methyl- l-cysteine with deuterium or tritium of solvents. The rate of α-hydrogen exchange with deuterium was about 40 times faster than that of the elimination reactions. The deuterium and tritium were exchanged also with the α- and β-hydrogens of the straight-chain amino acids which do not undergo the elimination: l-alanine, l-α-aminobutyrate, l-norvaline, and l-norleucine. No exchange occurs for the d-isomers, acidic l-amino acids, basic l-amino acids, and branched-chain l-amino acids, although α-hydrogen of glycine, l-tryptophan, and l-phenylalanine is exchanged slowly. These enzymatic hydrogen-exchange reactions facilitate specific labeling of the l-amino acids with deuterium and tritium.