Enzymatic synthesis of dopamine ring labeled with hydrogen isotopes

The chemo- enzymatic synthesis of labeled l-amino acids and some of their derivatives

This review compiles the combined chemical and enzymatic synthesis of aromatic l-amino acids (l-phenylalanine, l-tyrosine, l-DOPA, l-tryptophan, and their derivatives and precursors) specifically labeled with carbon and hydrogen isotopes, which were elaborated in our research group by the past 20 years. These compounds could be then employed to characterize the mechanisms of enzymatic reactions via kinetic and solvent isotope effects methods.

Hydrogen/deuterium exchange of cross-linkable α-amino acid derivatives in deuterated triflic acid

In this paper we report here a hydrogen/deuterium exchange (H/D exchange) of cross-linkable α-amino acid derivatives with deuterated trifluoromethanesulfonic acid (TfOD). H/D exchange with TfOD was easily applied to o-catechol containing phenylalanine (DOPA) within an hour. A partial H/D exchange was observed for trifluoromethyldiazirinyl (TFMD) phenylalanine derivatives. N-Acetyl-protected natural aromatic α-amino acids (Tyr and Trp) were more effective in H/D exchange than unprotected ones. The N-acetylated TFMD phenylalanine derivative afforded slightly higher H/D exchange than unprotected derivatives. An effective post-deuteration method for cross-linkable α-amino acid derivatives will be useful for the analysis of biological functions of bioactive peptides and proteins by mass spectrometry.

Studies on enzymatic oxidation of 3',4'-dihydroxy-l-phenylalanine to dopachrome using kinetic isotope effect methods

We report the studies on the mechanism of oxidation of 3',4'-dihydroxy-l-phenylalanine (l-DOPA) to neurotoxic dopachrome catalyzed by enzyme horseradish peroxidase (EC 1.11.1.7) using the kinetic (KIE), and solvent (SIE), isotope effect methods. For kinetic studies two specifically deuterated isotopomers: [2',5',6'-2H3]-l-DOPA was synthesized by the acid catalyzed isotopic exchange between native l-DOPA and heavy water, and [5'-2H]-l-DOPA was synthesized in two step reaction. The first step involved acid catalyzed isotopic exchange between l-tyrosine and deuterated water and resulting product [3',5'-2H2]-l-tyrosine was hydroxylated by enzyme tyrosinase (EC 1.14.18.1). The values of deuterium KIEs and SIE's in the enzymatic oxidation of l-DOPA and its isotopomers are determined using non-competitive spectrophotometric method. The measured values were: KIE on Vmax (1.1 and 2.2) and KIE on Vmax/KM (1.7 and 3.2) for [2',5',6'-2H3]-l-DOPA and [5'-2H]-l-DOPA, respectively, while the corresponding values of SIE were: SIE on Vmax (2.1, 2.4, and 2.1) and SIE on Vmax/KM (1.3. 1.6, and 1.1) for l-DOPA, [2',5',6'-2H3]-l-DOPA, and [5'-2H]-l-DOPA, respectively. The size of KIE and SIE, typical for secondary isotope effects indicate that both the solvent and presence of deuterium at the 2'-, 5', and 6'-positions of l-DOPA has the little impact on the enzymatic oxidation of this compound.