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Compound-specific Nitrogen Isotope Analysis of D-alanine, L-alanine, and Valine: Application of Diastereomer Separation to delta15N and Microbial Peptidoglycan Studies

Compound-specific Nitrogen Isotope Analysis of D-alanine, L-alanine, and Valine: Application of Diastereomer Separation to delta15N and Microbial Peptidoglycan Studies

Yoshinori Takano, Yoshito Chikaraishi, Nanako O Ogawa, Hiroshi Kitazato, Naohiko Ohkouchi

Anal Chem. 2009 Jan 1;81(1):394-9.

PMID: 19061396

Abstract:

We have developed an analytical method to determine the compound-specific nitrogen isotope compositions of individual amino acid enantiomers using gas chromatography/combustion/isotope ratio mass spectrometry. A novel derivatization of amino acid diastereomers by optically active (R)-(-)-2-butanol or (S)-(+)-2-butanol offers two advantages for nitrogen isotope analysis. First, chromatographic chiral separation can be achieved without the use of chiral stationary-phase columns. Second, the elution order of these compounds on the chromatogram can be switched by a designated esterification reaction. We applied the method to the compound-specific nitrogen isotope analysis of D- and L-alanine in a peptidoglycan derived from the cell walls of cultured bacteria (Firmicutes and Actinobacteria; Enterococcus faecalis, Staphylococcus aureus, Staphylococcus staphylolyticus, Lactobacillus acidophilus, Bacillus subtilis, Micrococcus luteus, and Streptomyces sp.), natural whole bacterial cells (Bacillus subtilis var. natto), (pseudo)-peptidoglycan from archaea (Methanobacterium sp.), and cell wall from eukaryota (Saccharomyces cerevisiae). We observed statistically significant differences in nitrogen isotopic compositions; e.g., delta15N ( per thousand vs air) in Staphylococcus staphylolyticus for d-alanine (19.2 +/- 0.5 per thousand, n = 4) and L-alanine (21.3 +/- 0.8 per thousand, n = 4) and in Bacillus subtilis for D-alanine (6.2 +/- 0.2 per thousand, n = 3) and L-alanine (8.2 +/- 0.4 per thousand, n = 3). These results suggest that enzymatic reaction pathways, including the alanine racemase reaction, produce a nitrogen isotopic difference in amino acid enantiomers, resulting in 15N-depleted D-alanine. This method is expected to facilitate compound-specific nitrogen isotope studies of amino acid stereoisomers.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
LS741329	Peptidoglycan from Methanobacterium sp.			Price

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