Na+ Transport by a Sodium Ion Pump Rhodopsin is Resistant to Environmental Change: A Comparison of the Photocycles of the Na+ and Li+ Transport Processes

摘要

Krokinobacter rhodopsin 2 (KR2) is a light-driven sodium ion pump. Although the photocycle of solubilized KR2 in LiCl solution is much longer than in NaCl, it effectively transports Li+ as Na+. This seems contradictory, because the rate of the photocycle determines the turnover speed of the pump. Here, we revealed that the photocycles in liposomes and E. coli membrane are similar between NaCl and LiCl. This is consistent with the comparable Na+ and Li+ pump efficiencies, and KR2 has a faster turnover of Na+ pump, which is resistant to environmental change.