Kinetic and solvent isotope effects on biotransformation of aromatic amino acids and their derivatives

• Published in: Journal of labelled compounds & radiopharmaceuticals 2016-12, Vol.59 (14), p.627-634
• Main Authors: Kańska, Marianna, Jemielity, Jacek, Pająk, Małgorzata, Pałka, Katarzyna, Podsadni, Katarzyna, Winnicka, Elżbieta
• Format: Article
• Language: English
• Subjects: Amino acids; Amino Acids, Aromatic - chemistry; Amino Acids, Aromatic - metabolism; Animals; Biotransformation; Dehydrogenases; DOPAL; Enzymes; isotope effects; Isotopes - chemistry; Kinetics; l-DOPA; l-phenylalanine; l-tryptophan; Metabolism; Metabolites; Rabbits; Solvents - chemistry; Studies
• ISSN: 0362-4803; 1099-1344
• DOI: 10.1002/jlcr.3419

Aromatic amino acids such as l‐phenylalanine, l‐tryptophan, 3′,4′‐dihydroxy‐l‐phenylalanine (l‐DOPA), and their derivatives 3′,4′‐dihydroxyphenylacelaldehyde (DOPAL) and 3′,4′‐dihydroxyphenylethanol (DOPET), play an essential role in human metabolic processes. Incorrect or slow biotransformation of these compounds leads to some metabolic dysfunctions and in some cases to some neurodegenerative diseases. Therefore, studies of the biotransformation mechanisms of these metabolites draw biochemists' and medical researchers' attention. This study investigates the mechanisms of biotransformation of the aforementioned compounds using kinetic (KIE) and solvent (SIE) isotope effect methods. The overview presents the results and the numerical values of KIE and SIE methods, obtained in the study of biotransformation of l‐phenylalanine, 5′‐chloro‐l‐tryptophan, and l‐DOPA, catalyzed by the enzymes from the lyases group (phenylalanine ammonia lyase, tryptophan indole‐lyase, and tyrosine decarboxylase). Deuterium KIE was also determined during the deamination of 2′‐chloro‐l‐phenylalanine in the presence of the enzyme l‐phenylalanine dehydrogenase, as well as in the conversion of DOPAL into DOPET catalyzed by the enzyme alcohol dehydrogenase. The values of KIE and SIE have been determined using a noncompetitive spectrophotometric and a competitive (combined with internal radioactivity standard) radiometric methods. Kinetic isotope effect and Solvent isotope effect were determined for enzymatic reaction of deamination of l‐phenylalanine, decarboxylation of l‐DOPA, and 5′‐chloro‐l‐tryptophan, catalyzed by liases, as well as for oxidative deamination of 2′‐chloro‐l‐phenylalanine and conversion of 3,4‐dihydroxyphenylacelaldehyde to 3,4‐dihydroxyphenylethanol catalyzed by dehydrogenases. For these studies the labeled with 2H‐, 3H‐ and 14C‐isotopomers of aforementioned mentioned compounds were used.