title: Application of liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the analysis of stable isotope enrichments of phenylalanine and tyrosine.
abstract: Whole-body protein synthesis and breakdown are measured by a combined tracer infusion protocol with the stable isotope amino acids L-[ring-(2)H(5)]-phenylalanine, L-[ring-(2)H(2)]-tyrosine and L-[ring-(2)H(4)]-tyrosine that enable the measurement of the phenylalanine to tyrosine conversion rate. We describe a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the measurement of very low tracer-tracee ratios (TTR) of the amino acids L-phenylalanine and L-tyrosine in human plasma. TTR calibration curves of the tracers L-[ring-(2)H(5)]-phenylalanine, L-[ring-(2)H(2)]-tyrosine and L-[ring-(2)H(4)]-tyrosine were linear (r(2)>0.99) in the range between 0.01% and 5.0% TTR and lowest measurable TTR for the tracers was 0.01% at a physiological concentration of 60 microM. The method was applied successfully to plasma samples from a clinical study reaching a steady state enrichment plateau (mean+/-SD) of 3.33+/-0.19% for L-[ring-(2)H(5)]-phenylalanine, 2.40+/-0.43% for L-[ring-(2)H(2)]-tyrosine and 0.29+/-0.07% for L-[ring-(2)H(4)]-tyrosine, respectively. The LC-MS/MS method can be applied for measurement of very low plasma enrichments of phenylalanine and tyrosine for the determination of whole-body protein synthesis and breakdown rates in humans.
authors.affiliation: University of Arkansas for Medical Sciences (UAMS), Center for Translational Research in Aging & Longevity (CTRAL), Donald W. Reynolds Institute on Aging, Little Rock, AR 72205, USA. rjw.meesters@ctral.org
authors.forename: Roland J W
authors.initials: RJ
authors.lastname: Meesters
authors.forename: Robert R
authors.initials: RR
authors.lastname: Wolfe
authors.forename: Nicolaas E P
authors.initials: NE
authors.lastname: Deutz
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D010649:Phenylalanine / Q000737:chemistry*; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D014443:Tyrosine; D010649:Phenylalanine