Inhibition studies of soybean trypsin-like enzyme.

The results of inhibition studies of soybean trypsin-like enzyme (STLE) by substrate analogues (derivative of arginine) suggested that a net negative charge exists at or near the substrate binding region of the enzyme. On hydrolysis of substrates, this negative charge seems to repel the products from the substrate binding region and facilitate the turn-over of substrates. From the data on inhibition by various amidines, guanidines, and amines, some information about the structure of the hydrophobic binding pocket of STLE was obtained. The inactivation of STLE by irreversible inhibitors, diisopropylfluorophosphate (DFP) and tosyl-lysine chloromethyl ketone (Tos-Lys-CH2Cl), was decreased by competitive inhibitors. This means that these irreversible inhibitors bind with residues at the substrate binding region, probably serine and histidine residues, respectively.