Department of Physiology and Department of Microbiology, Immunology and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, California, 90095, USA.
Annu Rev Biochem. 2021 Jun 20;90:1-29. doi: 10.1146/annurev-biochem-011520-105008. Epub 2021 Jan 20.
Bacterial cytoplasmic membrane vesicles provide a unique experimental system for studying active transport. Vesicles are prepared by lysis of osmotically sensitized cells (i.e., protoplasts or spheroplasts) and comprise osmotically intact, unit-membrane-bound sacs that are approximately 0.5-1.0 μm in diameter and devoid of internal structure. Their metabolic activities are restricted to those provided by the enzymes of the membrane itself, and each vesicle is functional. The energy source for accumulation of a particular substrate can be determined by studying which compounds or experimental conditions drive solute accumulation, and metabolic conversion of the transported substrate or the energy source is minimal. These properties of the vesicle system constitute a considerable advantage over intact cells, as the system provides clear definition of the reactions involved in the transport process. This discussion is not intended as a general review but is concerned with respiration-dependent active transport in membrane vesicles from . Emphasis is placed on experimental observations demonstrating that respiratory energy is converted primarily into work in the form of a solute concentration gradient that is driven by a proton electrochemical gradient, as postulated by the chemiosmotic theory of Peter Mitchell.
细菌细胞质膜泡为研究主动运输提供了一个独特的实验系统。通过渗透压敏感细胞（即原生质体或球形体）的裂解制备囊泡，并包含渗透压完整、单位膜结合的囊泡，其直径约为 0.5-1.0 μm，且无内部结构。它们的代谢活性仅限于膜本身的酶所提供的活性，并且每个囊泡都是功能性的。可以通过研究哪些化合物或实验条件驱动溶质积累来确定特定底物积累的能量来源，并且被运输的底物或能量来源的代谢转化最小化。与完整细胞相比，囊泡系统的这些特性构成了相当大的优势，因为该系统为运输过程中涉及的反应提供了明确的定义。本文的讨论并非旨在进行一般性综述，而是关注于来自 的膜囊泡中依赖呼吸的主动运输。重点是实验观察结果，这些结果表明呼吸能量主要转化为质子电化学梯度驱动的溶质浓度梯度的功，正如彼得·米切尔的化学渗透理论所假设的那样。
