Influence of metal ions on the transport of ascorbate across membranes

The effect of Fe2+, Cu2+, Ca2+, and Mg2+ on the permeation of ascorbate across membranes of dipalmitoyllecithin (DPPC) vesicles was investigated. As in previous experiments, the spin label I (1,14) was used for monitoring this transport. While Mg2+ and Ca2+ exerted a small effect only, Fe2+ and Cu2+ increased considerably the reduction of the spin label. In the case of Fe2+, this is not only due to a higher permeation rate of ascorbate but is also caused by a permeation of Fe2+. As a matter of fact, the largest reduction of the spin label was obtained if Fe2+ alone was added to the spin labelled DPPC solution. The reduction of the spin label seems to depend on the redox potentials of the constituents.