Enzymatic Decarboxylation of Tyrosine and Phenylalanine To Enhance Volatility for High-Precision Isotopic Analysis

• Published in: Analytical chemistry (Washington) 2002-01, Vol.74 (2), p.479-483
• Main Authors: Ziadeh, Bassem I, Michaud, Anthony L, Saad, Nabil M. R, Lewis, Betty A, Rafii, Mahroukh, Pencharz, Paul B, Brenna, J. Thomas
• Format: Article
• Language: English
• Subjects: Amino Acids - analysis; Animals; Biological and medical sciences; Carboxy-Lyases - metabolism; Chemicals; Chromatography; Enzymes; Fundamental and applied biological sciences. Psychology; Humans; Isotopes - analysis; Mass Spectrometry; Methods; Molecular and cellular biology; Phenylalanine - metabolism; Scientific imaging; Tyrosine - metabolism
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac015558j

We present a rapid and selective method to increase the volatility of tyrosine and phenylalanine without adding derivative C for high-precision gas chromatography−continuous-flow isotope ratio mass spectrometry (GCC−IRMS) based on enzymatic decarboxylation to yield alkylamines and evaluated for 15N isotopic integrity. Purified tyrosine and phenylalanine were converted to tyramine and phenethylamine by tyrosine and phenylalanine decarboxylases, respectively. GC separation was achieved using a thick stationary phase (5-μm) capillary column. Recoveries were 95 ± 2%. The reproducibility of δ15N of tyramine and phenethylamine measured by GCC−IRMS averaged SD(δ15N) = 0.33‰. The absolute differences between δ15N of amino acids measured by elemental analyzer-IRMS and the alkylamines measured by GCC−IRMS was not significant. Phenethylamine and tyramine prepared from a mixture of 18 amino acids were extracted by ethanol with 95% recovery, and analysis yielded clean chromatograms and equivalent precision. These data indicate that enzymatic decarboxylation of phenylalanine and tyrosine is a convenient method to increase their volatility for continuous-flow isotopic analysis without introducing extraneous C or significant isotopic fractionation.