Insights Into Amino Acid Metabolism and Incorporation by Compound- Specific Carbon Isotope Analysis of three-Spined Sticklebacks

Interpretation of isotope data is of upmost importance in ecology to build sound models for the study of animal diets, migration patterns and physiology. However, our understanding of isotope fractionation and incorporation into different consumer tissues is still limited. We therefore measured the δ13C values of individual amino acids from muscle and liver tissue of three-spined sticklebacks (Gasterosteus aculeatus) over time in a controlled feeding experiment. The isotope signatures of amino acids in the liver quickly responded to even small shifts in dietary isotope compositions, whereas muscle tissue remained isotopically constant over time. No significant fractionation between diet and fish tissues was observed for half of the amino acids in both liver and muscle tissue, supporting the idea of direct nutrient routing on a protein rich diet. Small isotopic differences were observed for alanine, glycine and serine between diet and liver, indicating that metabolic processes such as glycolysis or gluconeogenesis can be tracked by the isotope signatures of their main substitutes. We demonstrate that compound-specific isotope analysis has great potential to investigate the main metabolic pathways of organisms and suggest further investigations using isotopically enriched materials to facilitate the correct interpretation of ecological field data.

δ13C compound-specific isotope analysis in organic compounds by GC/MC-ICPMS

The work demonstrates a novel analytical method for compound-specific carbon isotope analysis in organic compounds by gas chromatography hyphenated with MC-ICPMS.

Fate of free and bound phytol and tocopherols during fruit ripening of two Capsicum cultivars

Phytol and tocopherols and their fatty acid esters (PFAE and TFAE) are isoprenoid lipid components which can be found for instance in vegetables. Their behavior during maturation of fruits and vegetables could reveal valuable information on their biosynthetic formation and biological function. As pods of the genus Capsicum contain considerable amounts of both PFAE and TFAE, two cultivars (i.e. Capsicum annuum var. Forajido and Capsicum chinense var. Habanero) were grown in a greenhouse project. The date of flowering and fruit formation of each blossom was noted and fruits were harvested in four specific periods which corresponded with different stages of ripening, i.e. unripe, semi-ripe, ripe and overripe. Quantification by means of gas chromatography mass spectrometry and creation of development profiles strongly supported the suggestion that PFAE and TFAE were formed as storage molecules during fruit ripening and parallel degradation of chlorophyll. Additionally, compound-specific carbon isotope ratios (δ13C values (‰)) of originally in PFAE and chlorophyll bound phytol ultimately proved that PFAE, besides tocopherols, serve as sink for the cytotoxic phytol moiety released from chlorophyll degradation during fruit ripening. Furthermore, color measurements were successfully implemented to simplify the usually cumbersome separation of chili fruits into different ripening degrees.