Human hepatic N-acetylglutamate content and N-acetylglutamate synthase activity. Determination by stable isotope dilution.
N-Acetyl-L-glutamate (N-acetylglutamate) content and N-acetylglutamate synthase activity ranges were established in human liver tissue homogenates by stable isotope dilution. The methods employ N-[methyl-2H3]acetyl[15N]glutamate as internal standard, extraction of N-acetylglutamate by anion-exchange technique and its determination by g.l.c.-mass spectrometry by using selected ion monitoring. Hepatic N-acetylglutamate content in 16 different human livers, normal in structure and function, ranged from 6.8 to 59.7 nmol/g wet wt. (25.0 +/- 13.4 mean +/- S.D.) or from 64.6 to 497.6 nmol/g of protein (223.2 +/- 104.2 mean +/- S.D.). In vitro, N-acetylglutamate synthase activity in liver tissue homogenate ranged from 44.5 to 374.5 (132.0 +/- 90.6 mean +/- S.D.) nmol/min per g wet wt. or from 491.7 to 3416.9 (1159.6 +/- 751.1 mean +/- S.D.) nmol/min per g of protein. No correlation was found between hepatic N-acetylglutamate concentrations and the respective maximal enzymic activities in vitro of N-acetylglutamate synthase. The marked variability in this system among individual livers may reflect its regulatory role in ureagenesis.
Tuchman
M
M
Department of Pediatrics, University of Minnesota, Minneapolis 55455.
Holzknecht
R A
RA
D000123:Acetyltransferases / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D051046:Amino-Acid N-Acetyltransferase; D002648:Child; D002675:Child, Preschool; D002852:Chromatography, Ion Exchange; D008401:Gas Chromatography-Mass Spectrometry; D005971:Glutamates / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D007201:Indicator Dilution Techniques; D008099:Liver / Q000737:chemistry* / Q000201:enzymology; D008875:Middle Aged; D012016:Reference Values
D005971:Glutamates; D000123:Acetyltransferases; D051046:Amino-Acid N-Acetyltransferase; C494874:NAGS protein, human; C016195:N-acetylglutamic acid