Copper Transport Across Pea Thylakoid Membranes

The initial rate of Cu^2+ movement across the thylakoid membrane of pea (Pisum sativum) chloroplasts was directly measured by stopped-flow spectrofluorometry using membranes loaded with the Cu^2+-sensitive fluorophore Phen Green SK. Cu^2+ transport was rapid, reaching completion within 0.5 s. The initial rate of uptake was dependent upon Cu^2+ concentration and saturated at about 0.6 (mu)M total Cu^2+. Cu^2+ uptake was maximal at a thylakoid lumen pH of 7.0. Cu^2+ transport was inhibited by Zn2+ but was largely unaffected by Mn^2+ and Cu+. Zn^2+ inhibited Cu^2+ transport to a maximum of 60%, indicating that there may be more than one transporter for copper in pea thylakoid membranes.