The interaction between Urinary Trypsin Inhibitor（UTI） and 1-anilino-8-naphthalisene Sulfonate（ANS） was investigated by fluorescence spectrum

Isothermal Titration Calorimetry（ITC） and molecular model.The results of the three experiments identically revealed the presence of four specific binding sites on UTI for ANS

and the interaction between UTI and ANS in the four specific binding sites were driven mainly by electrostatic interaction.The four binding sites were named as site Ⅰ

Ⅱ

Ⅲ and Ⅳ respectively.Site Ⅰ was located in domain Ⅱ and near to Trp98;site Ⅱ were located in the interaction region of the two domains;site Ⅲ and site Ⅳ were located in domain Ⅰ.The results indicated there were four hydrophobic patches in UTI.But the data of ITC experiments showed the presence of other five nonspecific binding sites.The interaction between UTI and ANS in the five nonspecific binding sites were driven mainly by the formation of salt band between the sulfonates of ANS and positive residues on the surface of UTI

which indicated there were five positive residues in the surface of UTI molecular in the neutral buffer.