Comparison of 15N-labelled glycine, aspartate, valine and leucine for measurement of whole-body protein turnover.
1. Whole-body protein turnover was measured in rats by constant infusion of 15N-labelled glycine, aspartate, valine and leucine and measuring the enrichment of hepatic and renal urea and ammonia nitrogen. 2. The values obtained with [15N]glycine were comparable with values reported with methods based on different assumptions. 3. [15N]Aspartate gave rise to an increased enrichment of urea and ammonia and hence to lower protein-turnover rates. 4. [15N]Valine and [15N]leucine gave low enrichments of nitrogenous end products and hence to high protein-turnover rates. 5. All 15N-labelled amino acids are not equally suitable for measuring whole-body protein turnover by the end-product method. The relative amounts of 15N going to the end products can be predicted from the known individual metabolism of aspartate and the branched-chain amino acids.
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D007930:Leucine / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D009590:Nitrogen Radioisotopes; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D014508:Urea / Q000378:metabolism; D014633:Valine / Q000378:metabolism*; D014915:Whole-Body Counting
D009590:Nitrogen Radioisotopes; D011506:Proteins; D001224:Aspartic Acid; D000641:Ammonia; D014508:Urea; D007930:Leucine; D014633:Valine; D005998:Glycine