Use of stable isotopes to measure de novo synthesis and turnover of amino acid-C and -N in mixed micro-organisms from the sheep rumen in vitro

Atasoglu C., GULIYE A., WALLACE R.

BRITISH JOURNAL OF NUTRITION, vol.91, no.2, pp.253-261, 2004 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 91 Issue: 2
  • Publication Date: 2004
  • Doi Number: 10.1079/bjn20031040
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.253-261
  • Çanakkale Onsekiz Mart University Affiliated: Yes


Protein synthesis and turnover in ruminal micro-organisms were assessed by stable-isotope methods in order to follow independently the fate of amino acid (AA)-C and -N in different AA. Rumen fluid taken from sheep receiving a grass hay-concentrate diet were strained and incubated in vitro with starch - cellobiose - xylose in the presence of NH3 and 5 g algal protein hydrolysate (APH)/l, in incubations where the labels were (NH3)-N-15, [N-15]APH- or [C-13]APH. Total N-15 incorporation was calculated from separate incubations with (NH3)-N-15 and [N-15]APH, and net N synthesis from the increase in AA in protein-bound material. The large difference between total and net AA synthesis indicated that substantial turnover of microbial protein occurred, averaging 3.5 %/h. Soluble AA-N was incorporated on average more extensively than soluble AA-C (70 v. 50 % respectively, P= 0.001); however, incorporation of individual AA varied. Ninety percent of phenylalanine-C was derived from the C-skeleton of soluble AA, whereas the incorporation of phenylalanine-N was 72 %. In contrast, only 15 % aspartate-C + asparagine-C was incorporated, while 45 % aspartate-N + asparagine-N was incorporated. Deconvolution analysis of mass spectra indicated substantial exchange of carboxyl groups in several AA before incorporation and a condensation of unidentified C-2 and C-4 intermediates during isoleucine metabolism. The present results demonstrate that differential labelling with stable isotopes is a way in which fluxes of AA synthesis and degradation, their biosynthetic routes, and separate fates of AA-C and -N can be determined in a mixed microbial population.