Energetics of protein transport across biological membranes:: A study of the thylakoid ΔpH-dependent/cpTat pathway

被引:77
作者
Alder, NN [1 ]
Theg, SM [1 ]
机构
[1] Univ Calif Davis, Div Biol Sci, Plant Biol Sect, Davis, CA 95616 USA
基金
美国国家科学基金会;
关键词
D O I
10.1016/S0092-8674(03)00032-1
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Among the pathways for protein translocation across biological membranes, the DeltapH-dependent/Tat system is unusual in its sole reliance upon the transmembrane pH gradient to drive protein transport. The free energy cost of protein translocation via the chloroplast DeltapH-dependent/Tat pathway was measured by conducting in vitro transport assays with isolated thylakoids while concurrently monitoring energetic parameters. These experiments revealed a substrate-specific energetic barrier to cpTat-mediated transport as well as direct utilization of protons from the gradient, consistent with a H+/protein antiporter mechanism. The magnitude of proton flux was assayed by four independent approaches and averaged 7.9 x 10(4) protons released from the gradient per transported protein. This corresponds to a DeltaG(transport) of 6.9 x 10(5) W-mol protein translocated(-1), representing the utilization of an energetic equivalent of 10(4) molecules of ATP. At this cost, we estimate that the DeltapH-dependent/cpTat pathway utilizes approximately 3% of the total energy output of the chloroplast.
引用
收藏
页码:231 / 242
页数:12
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