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摘要
The urea-induced dissociation of nerve growth factor from venom of Chinese cobra ((c)NGF) was studied by intrinsic fluorescence emission spectra, SEC, urea-gradient polyacrylamide gel electrophoresis, assays of biological activity and thermodynamic parameters. The results showed that when urea concentration was lower than or equal to 4.0 mol L-1 or higher than or equal to 8.0 mol L-1, (c)NGF existed only in native homodimer form or monomer form, respectively; whereas when urea concentration was higher than 4.0 mol L-1 and lower than 8.0 mol L-1, they existed simultaneously in the native homodimer and monomer forms and the former decreased, while the latter increased with the increase in urea concentration. Based on the association-dissociation equilibrium between (c)NGF and urea molecules, an equation, which includes two characteristic dissociation parameters K and a dagger m, was presented to describe the urea-induced dissociation process of (c)NGF. As the reaction temperature increased from 15 to 35 A degrees C, positive enthalpy and entropy changes were observed, and the parameter K increased from 2.72 x 10(-13) to 5.18 x 10(-12) (L mol(-1)), while the parameters a dagger m and a dagger G, respectively, decreased from 10.18 to 8.42 and from -10.27 to -18.67 (kJ mol(-1)), which means that the urea-induced dissociation of (c)NGF was spontaneous and entropy-driven and the higher temperature was favorable for the dissociation process. Using the procedures and equations mentioned in the paper, the urea-induced dissociation of
