It has been reported that the carboxyl terminal of Asp32 can act on HNe1(His64) by strengthening the negative charge on the imidazole ring of His64[24] and two hydrogen bonds of Asp32 and His64 are strong and stable enough to exist in all three catalytic states and in the binding and catalytic steps [14]. The carboxylate anion of Asp32 increases the proton affinity of the imidazole ring of His64 to an extent. Meanwhile, His64 captures the proton from the hydroxyl group of Ser221 and Ser221 finally attacks the peptide bond. In this study, Ile31 was replaced by Leu31, which led to an increase in catalytic efficiency due to the larger Kcat. The results of MD simulation in the present work indicated that the carboxyl terminal of Asp32 could act on ND1 (His64) easier and thus the negative charge on the imidazole ring of His64 was strengthened when the substrate was in complex with I31L mutant. This strong negative charge could increase the alkalinity of NE2 (His64). At the same time, with the aid of the substrate's inductive interaction, the strong attraction of NE2 (His64) for the proton of hydroxyl group of Ser221 caused strong nucleophilic attack. Thus, the rate of the conversion of substrate into product was increased, namely, the catalytic efficiency was improved.