The Mechanism Of Protein Degradation By Endopeptidases In Ensiled Alfalfa

Ensiling alfafalfa(Medicago sativa L.) forage is an altnative to avoiding nutrients loss in hay-making. However, during the procedure of ensiling, most of true protein was hydrolyzed to non-protein nitrogen (NPN) by the proteases. The NPN usually is not efficiently utilized by animals This greatly reduces the nutritional value of alfalfa silage and utilization efficiency.AS the plant proteases play a main role in the process of true protein degradation, characteristics of endopeptidases in alfalfa and their role in protein degradation of silage were investigated in this paper by using the previously fermented alfalfa Juice (PFJ). The role of proteases on the formation of NPN during proteolysis of fermented alfalfa juice was determined by adding the protease inhibitors and a control group before making of PFJ. Study results indicated1) There are four type endopeptidase in alfalfa:Serine protease, aspartic protease, metalloproteinase and cysteine protease;2) 5mM of PMSF,0.1 mM of pepstatin A,5mM ofl,10-phenantroline and 0.1 mM of E-64, could completely inhibited the activity of serine protease, aspartic protease, metallo-proteinase and cysteine protease;3) Metallo-peptidase was the principal endopeptidase contributing the formation of NH3-N and cysteine peptidase did not play a role on the formation of NH3-N. The importance of the three endopeptidases contributing to the formation of AA-N was metallo-, cysteine, and serine peptidase in turn. Aspartic peptidase made little contribution on the formation of NH3-N and AA-N. degradation of protein into peptides was attributed to aspartic-and cysteine peptidases. It was conclude that Metallo-and cysteine peptidases were the principle pepdidases for hydrolyzing forage protein into NPN in the process of ensiling and endopeptidases might not play a main role on proteolysis in ensiled forages.