Ferrous Ion Transport across Chloroplast Inner Envelope Membranes1

AUTOR(ES)

Shingles, Richard

FONTE

American Society of Plant Physiologists

RESUMO

The initial rate of Fe2+ movement across the inner envelope membrane of pea (Pisum sativum) chloroplasts was directly measured by stopped-flow spectrofluorometry using membrane vesicles loaded with the Fe2+-sensitive fluorophore, Phen Green SK. The rate of Fe2+ transport was rapid, coming to equilibrium within 3s. The maximal rate and concentration dependence of Fe2+ transport in predominantly right-side-out vesicles were nearly equivalent to those measured in largely inside-out vesicles. Fe2+ transport was stimulated by an inwardly directed electrochemical proton gradient across right-side-out vesicles, an effect that was diminished by the addition of valinomycin in the presence of K+. Fe2+ transport was inhibited by Zn2+, in a competitive manner, as well as by Cu2+ and Mn2+. These results indicate that inward-directed Fe2+ transport across the chloroplast inner envelope occurs by a potential-stimulated uniport mechanism.

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