Partial isolation and characterisation of Medicago sativa leaf proteases

Proteolysis of leaf proteins by endogenous leaf proteases between the time of harvest and the early stages of processing accounts for substantial losses (up to 40%) in recoverable protein from Medicago sativa [lucerne (alfalfa)] leaves. To study this problem, the proteolytic enzymes from M. sativa were partially purified by ammonium sulphate fractionation and gel filtration. Carboxypeptidase, aminopeptidase and total protease activities were measured. Addition of the herbicide simazine to leaf extract inhibited the aminopeptidase and total protease activity, but had no effect on the carboxypeptidase activity. The extent of proteolysis in leaf extracts was found to be dependent on pH, temperature and time of handling and it was concluded that these factors were the most effective means of controlling proteolytic activity.