Contribution of proteolytic and metabolic sources to hepatic glutamine by 2H NMR analysis of urinary phenylacetylglutamine 2H-enrichment from 2H2O

Proteolytic and cataplerotic sources of hepatic glutamine were determined by 2H NMR analysis of urinary phenylacetylglutamine (PAGN) 2H-enrichments in eight healthy subjects after 2H2O and phenylbutyric acid ingestion. Body water enrichment was 0.49±0.03%. PAGN was enriched to lower levels with significant differences between the various glutamine positions. PAGN position 2 enrichment=0.33±0.02%; 3R=0.27±0.02%; 3S=0.27±0.02% and position 4=0.17±0.01%. Position 3R,S enrichments are conditional with the net conversion of citrate to glutamate and are therefore markers of cataplerosis. From the ratio of positions 3R,S to body water enrichment, 55±3% of hepatic glutamine was derived from cataplerosis and 45±3% from proteolysis. In conclusion, enrichment of PAGN 3R,S hydrogens relative to that of body water reflects the contribution of cataplerotic and proteolytic sources to hepatic glutamine.