The kinetic and solvent deuterium isotope effects in the 4- and 5-positions of the indole ring on the enzymatic decomposition of L-tryptophan.

The kinetic and solvent deuterium isotope effects in the 4- and 5-positions of the indole ring on the enzymatic decomposition of l-tryptophan catalysed by the enzyme TPase (EC. 4.1.99.1) were determined. The isotope effects were investigated by the non-competitive method using [4'-(2)H]-l-tryptophan, which was enriched in deuterium in 70% in the 4-position. The numerical values of isotope effects for 100% enrichment in deuterated label in that position were calculated by approximation. Those same isotope effects were determined for [5'-(2)H]-l-tryptophan fully deuteriated in the 5' -position.