Abstract
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.
Original language | English |
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Pages (from-to) | 253-261 |
Number of pages | 9 |
Journal | British Journal of Nutrition |
Volume | 91 |
Issue number | 2 |
DOIs | |
Publication status | Published - Feb 2004 |
Keywords
- amino acids
- carbon skeletons
- rumen
- sheep
- volatile fatty acids
- microbial-growth
- phenylacetic acid
- ruminal bacteria
- 2,2'-diaminopimelic acid
- nitrogen-metabolism
- anaerobic bacteria
- invitro
- peptides
- protein