5:15 PM - 6:45 PM
[MIS14-P08] Assessing anaerobic metabolism: insights from compound-specific isotope analysis of amino acids
Keywords:isotopic fractionation factors, deamination, nitrogen
Compound-specific stable isotope analysis of amino acids in organisms has been employed as a tool to understand the material and energy cycles in samples at the level of organisms, ecosystems, and environments. This method is proposed by empirical observations that a universal isotopic enrichment in 15N is found in amino acids for diverse species. For instance, glutamic acid, a major amino acid, is degraded with enzymatic deamination (that shows isotopic enrichment), incorporated directly into the tricarboxylic acid cycle, and extracted energy, under aerobic metabolism in organisms. However, little knowledge is available for change in the isotopic enrichment associated with ‘anaerobic metabolism’ such as glycolysis and fermentation in organisms. Therefore, we investigated the isotopic fractionation factor (α) during the deamination of alanine, a representative amino acid, that is degraded with the enzyme alanine aminotransferase under anaerobic metabolism, and also conducted laboratory-cultured samples to see the change in the nitrogen isotope ratio of amino acids under anaerobic metabolisms. The eukaryote Saccharomyces cerevisiae and the bacteria Lactococcus lactis were incubated with organic substrates and were compared the isotope ratios of amino acids for the before and after experiments. We found negligible isotopic enrichment for glutamic acid while considerably large enrichment for alanine in the samples. Our results demonstrate that the activity of anaerobic metabolism is recorded in the isotope ratios of the latter amino acid, and suggest that the comparison of the isotope ratios between two metabolically different amino acids (i.e., alanine and glutamic acid) can be useful to quantify the balance of aerobic-anaerobic metabolism in biological, ecological, and environmental samples.