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15 N enrichment of ammonium, glutamine‐amide and urea, measured via mass isotopomer analysis of hexamethylenetetramine
Author(s) -
Yang Dawei,
Puchowicz Michelle A.,
David France,
Powers Lisa,
Halperin Mitchell L.,
Brunengraber Henri
Publication year - 1999
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(199911)34:11<1130::aid-jms871>3.0.co;2-y
Subject(s) - chemistry , hexamethylenetetramine , isotopomers , ammonium , urea , amide , chromatography , ammonia , methylamine , glutamine , metabolism , molecule , organic chemistry , amino acid , biochemistry
Ammonium is an important intermediate of protein metabolism and is a key component of acid–base balance. Investigations of the metabolism of NH 4 + in vivo using isotopic techniques are difficult because of the low concentration of NH 4 + in biological fluids and because of frequent artifactual isotopic dilution of the enrichment of NH 4 + during the assay. A new gas chromatographic mass spectrometric method was designed to monitor the 15 N enrichment and concentration of NH 4 + in vivo . These are both calculated from the mass isotopomer distribution of hexamethylenetetramine (HMT) formed by reacting NH 4 + with formaldehyde. The enrichment of NH 4 + is amplified four times since the HMT molecule contains four atoms of nitrogen derived from NH 4 + . This allows the measurement of low 15 N enrichment of NH 4 + , down to 0.1%. 15 N enrichment of urea and of the amide N of L ‐glutamine are measured by enzymatic release of NH 4 + and conversion of the latter to HMT. These new techniques facilitate in vivo investigations of the metabolism of NH 4 + and related compounds. Copyright © 1999 John Wiley & Sons, Ltd.