Kinetic Analysis of H+鈥揘a+ Selectivity in a Light-Driven Na+-Pumping Rhodopsin

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• 作者：Yoshitaka Kato ; Keiichi Inoue ; Hideki Kandori
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2015
• 出版时间：December 17, 2015
• 年：2015
• 卷：6
• 期：24
• 页码：5111-5115
• 全文大小：340K
• ISSN：1948-7185

文摘

Krokinobacter eikastus rhodopsin 2 (KR2) is a recently identified light-driven Na⁺ pump from a marine bacterium. KR2 pumps Na⁺ in NaCl solution but pumps H⁺ in the absence of Na⁺ and Li⁺. The Na⁺ transport mechanism in KR2 has been extensively studied, whereas understanding of the H⁺ transport mechanism is very limited. Here we studied ion uptake mechanisms and H⁺鈥揘a⁺ selectivity using flash photolysis. The results show that decay of the blue-shifted M intermediate is dependent on both [Na⁺] and [H⁺], indicating that KR2 competitively uptakes Na⁺ or H⁺ upon M decay. Comprehensive concentration dependence of Na⁺ and H⁺ revealed that the rate constant of H⁺ uptake (k_H) was much larger than that of Na⁺ uptake (k_Na) with a ratio (k_H/k_Na) of >10³. Therefore, KR2 pumps only H⁺ when Na⁺ and H⁺ concentrations are similar. On the contrary, KR2 pumps Na⁺ exclusively under physiological conditions in which [Na⁺] is much greater than [H⁺].