Submitted to: Conference on Rumen Function
Publication Type: Abstract Only
Publication Acceptance Date: November 16, 1995
Publication Date: N/A
Technical Abstract: Leaves of the perennial legume Astragalus cicer (cicer milkvetch) are known to contain a factor that inhibits cellulose digestion by adherent ruminal cellulolytic bacteria. We have isolated the active agent by ultrafiltration, alkaline treatment and isoelectric focusing of the aqueous phase remaining after boiling and ether extraction of ground leaves. The purified product contained 77% carbohydrate (primarily galactose and arabinose, and including 6% uronic acids), and 8% protein (particularly enriched in hydroxyproline and serine). Linkage analysis by GC/MS of methylated alditol acetates and by **13C-NMR revealed a predominance of beta-1,4-galactosyl and beta-1,3,6-galactosyl linkages, with arabinose, rhamnose, and glucose located primarily at chain termini. This polysaccharide structure suggests either a novel type of arabinogalactan (AG) or a mixture of Type I and Type II AGs. The agent was neutralized by the beta-glucosyl Yariv reagent (an arabinogalactan protein binding agent) but not by cellulose or by cells of Fibrobacter succinogenes or Ruminococcus flavefaciens. The data suggest that the agent inhibits cellulose digestion by interfering with the binding of cells to cellulose, without itself binding to either substrate.