Enzymatic subunit splitting of lupine storage proteins

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Abstract
The purified vicilin‐like and legumin‐like proteins, major storage globulins of lupine seeds, undergo partial proteolytic breakdown when self‐incubated at 37 °C under moderately alkaline pH. The splitting preferentially involves the high molecular weight subunits of the globulins. The whole globulin extract and the purified globulin fractions split benzoylarginine‐p‐nitroanilide (BAPA), a known substrate for endopeptidases. Further purification of globulins 4 and 8 by gel filtration at high ionic strength or by adsorption chromatography on Concanavalin‐A Sepharose removes only partially this activity and does not abolish self‐digestion. This activity is attributed to an endogenous endopeptidase associated to each globulin. BAPAase is inactive in the conditions of protein extraction and isolation and no significant modifications of the subunits of the storage proteins occurred during these steps.