並列摘要
Kinetic mechanism of staphylococcal nuclease folding/unfolding has been established and shown as follow: (The equation is abbreviated) where N represents native state and D_i is unfolded state. The number of protons t ransfer for each individual step are 0.8 for the transition of N ↔ D_1, 1.7 for D_1 ↔D_2 transition. There is no proton transfer dur ing the react ion of D_2 ↔ D_3. Based on the mutation experiments, we observed that E75 is responsible for the proton transfer of D_1 ↔ D_2 transition. The X-ray diffraction results show a local stable segment formed by the interactions among E75 and K9 & H121. This mini body may contribute about half of the protein maintaini ng force based on DSC measurements. These result s imply that the protein folding may be solve d by using kinetics an d site-directed mutagenesis.