Main content area

Energy-transducing thylakoid membranes remain highly impermeable to ions during protein translocation

Teter, S.A., Theg, S.M.
Proceedings of the National Academy of Sciences of the United States of America 1998 v.95 no.4 pp. 1590-1594
thylakoids, protein transport, plant proteins, Zea mays, carotenoids, absorbance, membrane potential, ion transport, electrophysiology, pH, gramicidin, light harvesting complex, oxygen evolving complex, photosynthetic reaction centers
We investigated the operation of a posttranslational protein translocation pathway to determine whether ions are excluded from the translocase during protein transport. The membrane capacitance during protein translocation across chloroplast thylakoid membranes was monitored via electric-field-indicating carotenoid electrochromic bandshift measurements. Evidence is presented that shows that the membrane ion conductance is not increased during the complete cycle of binding, transport, and substrate release by the delta pH-dependent translocase; i.e., the membrane remains ion-tight during protein translocation. We further demonstrate that a synthetic targeting peptide that directs proteins across this membrane does not gate translocation pores. We conclude that protein transport across the thylakoid membrane does not compromise its ability to maintain ion gradients and is, thus, unlikely to affect its functions in energy transduction.