Poster: Membrane transport

Abs # 179: Copper and Iron Transport Across Thylakoid Membranes

Presenter:	Wimmers, Larry E, lwimmers@towson.edu
Authors	Wimmers, Larry E (A)   Shingles, Richard  (B)   McCarty, Richard E (B)
Affiliations:	(A): Towson University (B): Johns Hopkins University

The initial rate of Cu²⁺ and Fe²⁺ movement across the thylakoid membranes of pea (Pisum sativum L.) and Arabidopsis thaliana chloroplasts was directly measured by stopped-flow spectrofluorometry using membranes loaded with the Cu²⁺ and Fe²⁺- sensitive fluorophore, Phen Green SK. The rate of transport was rapid coming to equilibrium within 1s for Cu²⁺ and within 3s for Fe²⁺. The initial rate of uptake was dependent upon metal ion concentration and was saturable with a KM of approximately 0.5 µM Cu²⁺ and 5.0 uM Fe²⁺. Fe²⁺ transport was inhibited over 50% in the presence of equimolar concentrations of other divalent cations (Mn²⁺, Cd²⁺, and Zn²⁺). However, Cu²⁺ transport was only inhibited by Zn²⁺. Under high concentrations of Zn²⁺ (10 µM) there was a component of Cu²⁺ transport that was insensitive to Zn²⁺. Differences in kinetic constants under high and low zinc conditions lead us to speculate that there may be more than one copper transporter in pea thylakoid membranes.