Characterization of proteolysis in alfalfa and red clover
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The loss of protein (proteolysis) during the ensiling of forage legumes is a severe problem. Alfalfa (Medicago sativa L.) will lose 44 to 87% of its protein during ensiling, whereas red clover (Trifolium pratense L.), a legume of similar protein content, will lose only 7 to 40%. Reasons for this difference in proteolysis are unknown. Research was conducted to determine and compare the general characteristics (rates, pH and temperature effects) of proteolysis in red clover and alfalfa extracts, and secondly to evaluate different in vitro test proteins to monitor legume proteolysis. Proteolytic rates of alfalfa and red clover extracts were not significantly different when either ribulose 1,5-biphosphate carboxylase/oxygenase (RubisCo) or bovine serum albumin (BSA) was used as the protein substrate; however, both legumes displayed significantly higher rates for the degradation of RubisCo than BSA (P < 0.10). The pH optima were 5.5 for both legumes when RubisCo was degraded, and 5.5 and 6 for alfalfa and red clover, respectively, when BSA was the substrate. Proteolysis in the legume extracts had similar pH and temperature stabilities and temperature optimum for the degradation of RubisCo. These data suggest that alfalfa and red clover have similar inherent proteolytic activity and cannot explain the difference in extent of proteolysis in the two silages