Phosphorylating electron-transferring particle

The employment of cell organelles has been limited to mitochondrial and microsomal fractions (Table 15). As early as 1976, Guilbault et al. coupled pig heart mitochondrial electron transfer particles (ETP) with an oxygen electrode. This development has been further pursued by Aizawa et al. (1980c). Decoupling of the electron transfer from oxidative phosphorylation makes ETP catalyze the following reactions ... 

The spatial separation between the components of the electron transport chain and the site of ATP synthesis was incompatible with simple interpretations of the chemical coupling hypothesis. In 1964, Paul Boyer suggested that conformational changes in components in the electron transport system consequent to electron transfer might be coupled to ATP formation, the conformational coupling hypothesis. No evidence for direct association has been forthcoming but conformational changes in the subunits of the FI particle are now included in the current mechanism for oxidative phosphorylation. 

Also procedures for the isolation of inside-out membranes, by French Press treatment of intact bacteria, have been described. In phototrophic organisms, these membranes are derived from the invaginations of the plasma membrane and are called chromatophores. These preparations have been extensively used for studies on light-dependent cyclic electron transfer and photophosphorylation. In non-phototrophic bacteria the resulting structures are often called inverted membranes or membrane particles, in analogy with sub-mitochondrial particles. Amongst others, these preparations have been isolated from Azotobacter vinelandii and E. coli. These inverted membranes can be used for the study of oxidative phosphorylation and the determination of H /e stoicheiometries since the enzymatic machinery for these processes is located on the external surface of these membranes. Also excretion of ions (like ) from intact cells can be studied conveniently in these preparations because these ions are accumulated in inverted membranes. 

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