title: Rates of proteolysis in the rumen of the soluble proteins casein, fraction I (18S) leaf protein, bovine serum albumin and bovine submaxillary mucoprotein.
abstract: The rate of proteolysis in the rumen was dependent on the soluble protein used. With a sheep on a hay + concentrate diet the rates (approximately Vmax) for casein, Fraction I leaf protein and bovine serum albumin were 16.5, 3.4 and 0.9 mg protein nitrogen/l per min respectively. Change of diet from hay + concentrate to fresh lucerne (Medicago sativa) increased the proteolytic rates for all three proteins. Bovine submaxillary mucoprotein degraded extremely slowly in the rumen at approximately 0.5-0.6 mg N/l per min and its sialic acid component was degraded at a similar rate to that of the protein chain. Uniformly 14C-labelled Fraction I leaf protein was used to demonstrate that in the presence of a second protein, competition for enzymic sites occurred. In Fraction I and bovine serum albumin mixtures, reduced rates for the individual proteins of the mixture were observed compared with the proteins treated separately. Treatment of bovine serum albumin with dithiothreitol (0.2 g/l) to cleave disulphide bridges increased the rates of proteolysis by as much as 8.5-fold.
mesh_terms: D000818:Animals; D002364:Caseins / Q000378:metabolism; D002417:Cattle; D004044:Dietary Proteins / Q000378:metabolism*; D004229:Dithiothreitol; D005260:Female; D006868:Hydrolysis; D009088:Mucoproteins / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D012417:Rumen / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000378:metabolism; D012756:Sheep; D012794:Sialic Acids / Q000378:metabolism
chemical_list: D002364:Caseins; D004044:Dietary Proteins; D009088:Mucoproteins; D010940:Plant Proteins; D012794:Sialic Acids; D012710:Serum Albumin, Bovine; D004229:Dithiothreitol