An endopeptidase in dormant lupin seeds

A new endopeptidase has been identified and partially purified from the albumin extract of dormant white lupin seeds. The enzyme is specific for the acid polypeptides of the subunits of the lupin legumin-like proteins; it acts on those present in the seeds of 12S, 7S and modified 7S legumin oligomers and on their immediate breakdown products, forming products with acid polypeptides of apparent Mrs of 31 000 and 29 000. The breakdown follows a cascade cooperativity and the choice of substrate depends on the type and amount of the polypeptides present. The enzyme is inhibited by Mn2+, Co2+, Zn2+ and its activity is increased by Ca2+. Preincubation for 18-24 hr at 4° is required before protease activity is observed. During this period the enzyme undergoes limited proteolysis. The enzyme studied differs from the endopeptidase specific to the acid polypeptides of 52 000 of 12S oligomers, also from dormant lupin seeds. The observed cascade cooperativity of the two endopeptidases is discussed.