Research-article| Volume 72, ISSUE 10, P2540-2548, October 1989

Metabolism of Peptides and Amino Acids During In Vitro Protein Degradation by Mixed Rumen Organisms1

  • Glen Broderick
    Corresponding author.
    US Dairy Forage Research Center, USDA-Agricultural Research Service, 1925 Linden Drive West, University of Wisconsin, Madison 53706
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  • Author Footnotes
    2 Present address: Cargill Research Farms, Box 301, Elk River, MN 55330.
    W. Michael Craig
    2 Present address: Cargill Research Farms, Box 301, Elk River, MN 55330.
    US Dairy Forage Research Center, USDA-Agricultural Research Service, 1925 Linden Drive West, University of Wisconsin, Madison 53706
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  • Author Footnotes
    1 Mention of commercial products in this paper does not constitute endorsement by the USDA or the ARS.
    2 Present address: Cargill Research Farms, Box 301, Elk River, MN 55330.
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      In vitro inoculum enriched with particle-associated organisms was prepared using rumen contents from a cow fed a 60% forage, 40% concentrate diet. Treatment of in vitro inoculum with cetyltrimethylamrnonium bromide was used to release intracellular free amino acids from mixed rumen organisms. Addition of 10 mM tosylarginine methyl ester, a competitive inhibitor of trypsin, decreased degradation rate and intracellular free amino acids in incubations containing either casein or serum albumin. Extracellular peptides increased rapidly to a maximum at 60 min in casein incubations but were not different from zero in albumin incubations. Accumulation of intracellular free amino acids was maximal at 60 min in casein and albumin incubations; the concentration observed with albumin was about one-fourth that with casein. Ammonia production from intact casein was slightly greater than that from acid and enzymatically hydrolyzed casein and about 80% greater than that from albumin. Ammonia production and appearance of extracellular free amino acids lagged behind accumulation of intracellular free amino acids. Results suggest that formation and metabolism of extracellular peptides are important in controlling the rate of protein degradation by mixed rumen organisms.


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