Novel approaches to manipulating proteolysis in ensiled perennial ryegrass (PRG) were investigated. The effects of the following on nitrogen (N) distribution in silage were investigated: E- 64, a specific cysteine-peptidase inhibitor (CPI); pepstatin A a specific aspartic-peptidase inhibitor; cystamine dihyrochloride (CYS) and N-ethylmaleimide, general CPIs, and formic acid (FA). Treatment with FA or CPIs reduced total soluble N, as a result of reduced proteolysis, and FA and CYS treatments increased peptide N concentrations (determined using fluroescamine or ninhydrin assays, and by amino acid analysis) compared to the control. Pepstatin A had little or no effect on the N constituents of silage. Characterisation of silage peptides using Sephadex G-25 suggested that they were predominantly di and tripeptides, with a small proportion of longer peptides (>7 amino acid residues). Forty additional compounds were screened for their efficacy as inhibitors of proteolysis in aqueous extracts of PRG. Five selected compounds were applied to PRG at ensilage: TPCK, a non specific CPI; chelators, 1,10-phenanthroline and 8-hydroxyquinoline (8-HQ); bestatin, a metallo-peptidase inhibitor; and N-acetyl-L-tyrosine ethyl ester (ATEE), a serine-peptidase inhibitor. When compared to the control, TPCK and 1,10- phenanthroline reduced total soluble N and increased peptide N concentrations; 8-HQ increased only peptide N concentrations. These chelators also restricted fermentation. The effects of Trypticase (peptides produced by enzymic hydrolysis of casein), silage extracts and N fractions prepared from silage extracts by cation exchange chromatography, as sources of N, on the growth of rumen bacteria, <I>Megasphaera elsdenii, Prevotella ruminicola</I> and <I>Selenomonas ruminantium, </I>supplied with glucose as an energy substrate <I>in vitro, </I>were investigated. No growth was observed on media containing extracts from silages produced in the presence of chelators but all bacteria grew on purified N fractions. Increasing silage peptide N therefore did not enhance microbial growth but for some treatments, silage N supported faster growth than Trypticase.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:307998 |
| Date | January 1996 |
| Creators | Nsereko, Victor Leonard Joseph |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU079015 |
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