X-Message-Number: 12291
Date: Fri, 20 Aug 1999 08:37:53 -0700 (PDT)
From: Doug Skrecky <>
Subject: could proanthocyanidins replace chemical fixation?

  Tanner GJ.  Moore AE.  Larkin PJ.
  Division of Plant Industry, Commonwealth Scientific and Industrial Research
  Organization, Canberra, Australia.
  Proanthocyanidins inhibit hydrolysis of leaf proteins by
  rumen microflora in vitro.
  British Journal of Nutrition.  71(6):947-58, 1994 Jun.
  Proanthocyanidins (condensed tannins; PA) purified from the
  leaves of forage legumes Trifolium arvense, Lotus pedunculatus, Lotus
  corniculatus, Dorycnium rectum, Coronilla varia, Onobrychis viciifolia, or
  Hedysarum coronarium, were added to soluble lucerne (Medicago sativa) leaf
  protein and incubated with strained rumen fluid in vitro. Fractions were
  collected and frozen immediately. Denatured proteins were fractionated by
  sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE),
  stained, and relative levels were quantified by densitometry. In the absence
  of PA the large subunit (LSU) of ribulose bisphosphate carboxylase (EC was susceptible to proteolysis by rumen microflora but the small
  subunit (SSU) resisted breakdown. PA purified from Onobrychis was added to
  soluble leaf protein, at PA: protein ratios between 1:1 and 1:20. The rate of
  proteolysis of LSU was significantly reduced at PA: protein ratios of 1:2 and
  1:1 (P < 0.001) and the rate of digestion was reduced by between 3- and
  21-fold. In separate experiments PA isolated from the range of species
  described was added to rumen fluid to give PA: protein ratios of 1:5. The
  addition of PA significantly reduced the rate of proteolysis of LSU, when
  compared with PA-free control. There were only small differences between PA
  from different species. The inhibitory effect of PA may have been due to PA
  binding to the dietary protein or to the rumen proteases, interfering with
  the action of proteases on susceptible sites within the substrate.

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