Aluminum Lon Removal from Monoaluminum Ovotransferrin by Pyrophosphate

The rates at which aluminum was removed from the N- and C-terminal monoaluminum ovotransferrins by pyrophosphate 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 addition of 0.1 mol/L chloride to the monoaluminum ovotransferrin solutions, whereas the rates of the first-order kinetics 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 affected by chloride than that of the C-terminal. In the experiment presumably the N-terminal site is apparently kinetically more labile than the C-terminal site.

Aluminum ion removal from monoaluminum ovotransferrin by pyrophosphate

The rates at which aluminum was removed from the N‐ and C‐terminal monoaluminum ovotransferrins by pyrophosphate were evaluated by UV difference spectra in 0.01 mol/L Hepes, pH=7.4 and at 37 °C. 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 addition of 0.1 mol/L chloride to the monoaluminum ovotransferrin solutions, whereas the rates of the first‐order kinetics are decreased for the C‐terminal binding site. The effect of chloride ionic strength causes a continuing increase on k_obs for the N‐ and C‐terminal binding sites. Moreover, the kinetics behavior of the N‐terminal is more easily affected by chloride than that of the C‐terminal. In the experiment presumably the N‐terminal site is apparently kinetically more labile than the C‐terminal site.