摘要
The rates at which aluminum was removed from the N- and C-terminal monoaluminum ovotransferrins by py-rophosphate were evaluated by UV difference spectra in 0.01 mol/L Hepes, pH=7.4 and at 37 ℃. Pesudo first-order rate constants as a function of pyrophosphate concentration were measured. The results indicate that the pathways of aluminum removal are different. For the N-terminal binding site, aluminum removal follows simple saturation kinetics, while the removal of aluminum from the C-terminal binding site reverts to the combination of saturation and first-order kinetics. The saturation component is consistent with a rate-limiting conformational change in the protein as has been reported. We propose that the first-order kinetics mechanism is attributed to a pre-equilibrium process. The rate constants of saturation kinetics are accelerated from both terminals with the addi-tion of 0.1 mol/L chloride to the monoaluminum ovotransferrin solutions, whereas the rates of the first-order kinet-ics are decreased for the C-terminal binding site. The effect of chloride ionic strength causes a continuing increase on kobs for the N- and C-terminal binding sites. Moreover, the kinetics behavior of the N-terminal is more easily af-fected by chloride than that of the C-terminal. In the experiment presumably the N-terminal site is apparently ki-netically more labile than the C-terminal site.
The rates at which aluminum was removed from the N- and C-terminal monoaluminum ovotransferrins by py-rophosphate were evaluated by UV difference spectra in 0.01 mol/L Hepes, pH=7.4 and at 37 ℃. Pesudo first-order rate constants as a function of pyrophosphate concentration were measured. The results indicate that the pathways of aluminum removal are different. For the N-terminal binding site, aluminum removal follows simple saturation kinetics, while the removal of aluminum from the C-terminal binding site reverts to the combination of saturation and first-order kinetics. The saturation component is consistent with a rate-limiting conformational change in the protein as has been reported. We propose that the first-order kinetics mechanism is attributed to a pre-equilibrium process. The rate constants of saturation kinetics are accelerated from both terminals with the addi-tion of 0.1 mol/L chloride to the monoaluminum ovotransferrin solutions, whereas the rates of the first-order kinet-ics are decreased for the C-terminal binding site. The effect of chloride ionic strength causes a continuing increase on kobs for the N- and C-terminal binding sites. Moreover, the kinetics behavior of the N-terminal is more easily af-fected by chloride than that of the C-terminal. In the experiment presumably the N-terminal site is apparently ki-netically more labile than the C-terminal site.
基金
Project supported by the National Natural Science Foundation of China (Nos. 20371031
20071022).
