Effect of a p-nitro group of phenyl-maltooligosaccharide substrate on the change of action specificity of lysine-modified porcine pancreatic alpha-amylase.

The effect of chemical modification of lysine residues on the activity of porcine pancreatic alpha-amylase (PPA) was examined, using p-nitrophenyl-alpha-D-maltoside, p-nitrophenyl-alpha-D-maltotrioside, phenyl-alpha-D-maltoside and phenyl-alpha-D-maltotrioside as substrates. Chemical modification of PPA with trinitrobenzenesulfonic acid enhanced the kcat/Km values for p-nitrophenyl substrates, but not for phenyl substrates. Thus, this effect is substituent selective. Considering the productive binding modes of substrates to PPA, the p-nitro group of the substrate and the modified lysine residues of the enzyme would non-ionically interact with each other to stabilize the productive binding mode.