The inhibitory effect of 0.19 alpha-amylase inhibitor (0.19 AI) from wheat kernel on the porcine pancreas alpha-amylase (PPA)-catalyzed hydrolysis of p-nitrophenyl-alpha-D-maltoside (pNP-G2) was examined. 0.19 AI is a homodimer of 26.6 kDa with 13.3-kDa subunits under the conditions used. The elution behaviors in gel filtration HPLC of PPA and 0.19 AI indicated that a PPA molecule bound with a 0.19 AI molecule (homodimer) at a molar ratio of 1:1. 0.19 AI inhibited PPA activity in a competitive manner with an inhibitor constant, K(i), of 57.3 nM at pH 6.9, 30 degrees C, and the binding between them was found to be endothermic and entropy-driven. The activation energy for the thermal inactivation of 0.19 AI was determined to be 87.0 kJ/mol, and the temperature, T(50), giving 50% inactivation in a 30-min incubation at pH 6.9 was 88.1 degrees C. The high inhibitory activity of 0.19 AI against PPA and its high thermal stability suggest its potential for use in the prevention and therapy of obesity and diabetes.