|Marini, Juan -|
Submitted to: Rapid Communications in Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 2011
Publication Date: May 15, 2011
Citation: Marini, J.C. 2011. Quantitative analysis of 15N labeled positional isomers of glutamine and citrulline via electrospray ionization tandem mass spectrometry of their dansyl derivatives. Rapid Communications in Mass Spectrometry. 25(9):1291-1296. Interpretive Summary: The study of amino acid metabolism relies on the ability to trace these metabolites through different pathways. The problem is that some amino acids derived part of their functional groups from different precursors, and the analytical techniques available do not permit to differentiate between these different precursors. In this work, I developed a liquid chromatography-mass spectrometry method to trace the different moieties of the amino acids citrulline and glutamine which has provided new insight on their synthesis and utilization. This novel analytical method has challenged the current assumption that glutamine is the precursor for citrulline (and thus arginine) synthesis, which will lead to a reevaluation of supplementation strategies aimed to increase arginine availability.
Technical Abstract: The enteral metabolism of glutamine and citrulline are intertwined because, while glutamine is one of the main fuel sources for the enterocyte, citrulline is one of its products. It has been shown that the administration of 15N labeled glutamine results in the incorporation of the 15N label into citrulline, but it is not clear which of the three nitrogen groups of citrulline is actually labeled. To determine the 15N enrichment of the positional isomers of glutamine and citrulline, a rapid LC/MS/MS method was developed. The amino acids were analyzed as their dansyl derivatives. The product ion resulting from the loss of –NH3 from the omega carbon allows for the determination of the enrichment of the ureido (citrulline) or amido groups (glutamine). The protonated pyrrolidine (citrulline) or 5-oxopyrrolidine (glutamine) product ion contains the 2-N (amino group) and is used to determine its enrichment. The method described showed no ion suppression and a wide dynamic range ranging from 1.3 picomol to 2 nanomol for citrulline. Background samples and standards resulted in enrichments not different from the theoretically expected. The enrichment curves for the different glutamine and citrulline isotopomers were linear (R2> 0.998) over the range of enrichments studied. The method developed provides an additional insight in the metabolism of glutamine and citrulline tracing the precursor-product relationship between these two amino acids.