Characterization of serine endopeptidases in alfalfa and its role on protein degradation of silage

Characteristics of serine endopeptidases in alfalfa (Medicago sativa) and its role in protein degradation of silage were investigated by using the previously fermented alfalfa juice (PFJ) in this paper. The role of serine protease on the formation of nonprotein nitrogen (NPN) during proteolysis of fermented alfalfa juice was determined by adding the serine protease inhibitors PMSF in PFJ. The results of this study indicated that the optimum pH and temperature of alfalfa serine endopeptidases were 6.6 and 45℃ respectively; adding 5 mmol/L PMSF could completely inhibit the activity of serine protease. In alfalfa silage fermentation process, compared with control (no PMSF), PMSF significantly (P0.01) increased the soluble protein content and decreased (P0.01) NPN content of each component in the fermented alfalfa juice(FJ). The study suggested that serine endopeptidases did not play a main role on the formation of NPN during proteolysis process of ensiled forages.