Lipoxygenases (LOX) are responsible for the beany flavor, which is the most important obstacle for the consumption of soybean [Glycine max. (L.) Merrill] products in Western countries. The Kunitz trypsin inhibitor (KTI) is responsible for 80% of the inhibition of tryptic activity in soybean seeds, and besides it can cause pancreatic hyperplasia in monogastric animals. These two traits are very important in soybean breeding programs that aim the improvement of soy protein quality. The objective of this study was to verify the influence of KTI on LOX levels in soybean seeds by analyzing the following genotypes: KTI+/LOX+, KTI+/LOX-, KTI-/LOX+ and KTI-/LOX-. LOX 1 and LOX 3 were identified by colorimetric, activity and electrophoretic assays. Protein content was determined by the bicinchoninic method for determination of LOX specific activity. For genotype KTI+/LOX+, LOX 1 specific activity was high varying from 177.92 to 206.94 AU/mg of protein and LOX 3 activity varied from 17.90 to 19.85 AU/mg of protein. No LOX activity was detected in genotypes KTI+/LOX- and KTI-/LOX-. For genotype KTI-/LOX+, LOX 1 activity varied from 117.24 to 124.64 AU/mg of protein, and the activity of LOX 3 from 17.35 to 20.29 AU/mg of protein. There was a reduction of 40% on LOX 1 specific activity and 1% for LOX 3 in the KTI-/LOX+ genotype in comparison to genotype KTI+/LOX+. These results indicate an inverse relationship between the presence of the Kunitz trypsin inhibitor in soybean seeds and lipoxygenase activity.
Glycine max; trypsin; protein; enzymatic activity; KTI
