ASSAY OF THE CONCENTRATION AND C-13-LABELING PATTERN OF PHENYLACETYLGLUTAMINE BY NUCLEAR-MAGNETIC-RESONANCE

Phenylacetate, derived from phenylalanine, is converted in human and primate liver to phenylacetylglutamine. The latter, which is excreted in urine, has been used to probe noninvasively the labeling pattern of liver citric acid cycle intermediates. We present nuclear magnetic resonance assays for the urinary concentration of phenylacetylglutamine and for the C-13-labeling pattern of its glutamine moiety. The concentration of phenylacetylglutamine is calculated from the natural C-13 signals of all carbons of its benzene ring and C-2 of its acetyl moiety. The limit of detection is 13 mu mol of unlabeled phenylacetylglutamine. The minimum amount of phenylacetylglutamine needed to determine a 1% enrichment of one of its carbons is 26 mu mol. The technique was tested by analyzing phenylacetylglutamine in the urine from monkeys infused with various C-13 tracers. The labeling patterns obtained agreed with theoretical calculations and patterns reported in phenylacetylglutamine and glutamine labeled from C-14 and C-13 tracers, respectively. (C) 1994 Academic Press, Inc.