Short-term metabolic fate of [13N]ammonia in rat liver in vivo.

摘要: The short-term metabolic fate of [13N]ammonia in the livers adult male, anesthetized rats was determined. Following a bolus injection tracer quantities into portal vein, single pass extraction approximately 93%, good agreement with portal-hepatic vein difference 90%. High performance liquid chromatographic analysis deproteinized liver samples indicated that labeled nitrogen is exchanged rapidly among components of: mitochondrial aspartate aminotransferase and glutamate dehydrogenase reactions cytoplasmic alanine (t1/2 for exchange label toward equilibrium on order seconds). Comparison specific activities ammonia suggests at 5 s most mitochondrial, whereas 60 93% cytosolic; this change presumably brought about by combined action cytosolic aminotransferases carrier malate-aspartate shuttle. Specific activity measurements glutamate, alanine, are accord proposal Williamson et al. (Williamson, D.H., Lopes-Vieira, O., Walker, B. (1967) Biochem. J. 104, 497-502) reaction thermodynamic equilibrium, but compartmented rat liver. Despite considerable citrulline early time points, no radioactivity (less than or equal to 0.25% total) detected carbamyl phosphate, suggesting very efficient conversion little free phosphate accumulating mitochondria. Our data also show some vein-derived metabolized glutamine liver, amount small (approximately 7% urea) part because synthetase located population perivenous cells "downstream" from urea cycle-containing periportal cells. Finally, evidence could be found participation purine nucleotide cycle production aspartate. present work continues emphasize usefulness studies under truly conditions, particularly when turnover times seconds.