A serine protease in soybean seeds that acts specifically on the native alpha subunit of beta-conglycinin.

A proteolytic activity directed against the alpha subunit of beta-conglycinin was detected in resting mature seeds of the soybean [Glycine max (L.) Merrill] cultivar Keburi. The relationship between pH and activity and the effect of protease inhibitors revealed that the enzyme was a neutral/alkaline serine protease. The proteolysis of the alpha subunit of beta-conglycinin yielded a specific product with a molecular weight of about 47,000, as determined by SDS-PAGE, but the enzyme had no activity against the beta subunit. The amino acid composition, the molecular weight and the amino-terminal amino acid sequence of the proteolytic product revealed that the action of the enzyme on the alpha subunit was specific, with cleavage occurring only at the R126-R127 peptide bond of the alpha subunit. These characteristics of the protease indicate that the enzyme is a novel protease that has not previously been recognized in soybean seeds.