Preparation of Highly Deuterated Phenylalanine, Alanine, Valine, and Leucine/Isoleucine Using Facultative Methylotrophic Bacterium ?revibacterium Methylicum

Abstract

Microbiological preparation of [²H]amino acids was performed by conversion of low molecular weight substrates ([U-²H]MeOH and ²H₂O) by Gram-positive aerobic facultative methylotrophic bacterium, Brevibacterium methylicum, being L-phenylalanine producer having ribulose-5-monophosphate (RuMP) cycle for carbon assimilation. For this purpose, the cells of the methylotroph with improved growth characteristics were used on minimal salt media M9 supplemented with 2% (v/v) [U-²H]MeOH and increasing gradient of ²?₂O concentration from 0; 24.5; 49.0; 73.5 up to 98% (v/v) ²?₂O. L-phenylalanine was isolated from the growth medium after adding 5 M ²HCl (in ²?₂?), pH = 2.0 by extraction with isopropanol and subsequent crystallization in ethanol (output 0.65 g/l). Alanine, valine, and leucine/isoleucine were produced and accumulated exogenously in amounts of 5–6 mmol in addition to the main product of biosynthesis. The method allows to obtain [²?]amino acids with different levels of deuterium enrichment, depending on ²?₂O concentration in growth media, from 17% ²? (2 deuterium atoms) (on the growth medium with 24.5% (v/v) ²?₂?) up to 75% ²? (6 deuterium atoms) (on the growth medium with 98% (v/v) ²?₂?) with introduction of deuterium to benzyl ?₆?₅??₂-fragment of molecule that is confirmed with the data of electron impact (EI) mass spectrometry analysis of methyl ethers of N-5-dimethylamino(naphthalene)-1-sulfochloride [²H]amino acids after the separation by reverse-phase HPLC.

Keywords: Brevibacterium methylicum, [U-²H]MeOH, heavy water, biosynthesis, [²H]amino acids, EI mass spectrometry, HPLC.