Isotope effects in the enzymatic oxidation of tryptamine to 3-indolyl-acetaldehyde

The reaction mechanisms of the enzymatic deamination of tryptamine catalysed by the enzyme monoamine oxidase (MAO, EC 1.4.3.4) were investigated using the kinetic isotope effect and solvent isotope effect methods. The numerical values of these deuterium effects in the (1S) and (1R) positions of tryptamine were determined using the non-competitive spectrophotometry. The deuterium-labelled isotopologue (1S)-²H]tryptamine was obtained in two steps by enzymatic coupling of indole with S-methyl-l-cysteine in a deuterated medium followed by enzymatic decarboxylation of the resulting 2-²H]-l-tryptophan. (1R)-²H]tryptamine was obtained by enzymatic decarboxylation of l-tryptophan in the fully deuterated medium.