Arnold F. Brodie

[22] Properties of energy-transducing systems in different types of membrane preparations from Mycobacterium phlei-preparation, resolution, and reconstitution

Publisher Summary Many bacterial systems have been used to study membrane-related phenomena, such as oxidative phosphorylation, electron transport, active transport of solutes, and membrane topology. However, with most systems, little is known about the nature and composition of membrane components or the vectorial orientation of the membrane structure. In contrast, the membrane structures obtained from Mycobacterium phlei have been characterized with regard to the nature of the respiratory chains, the sequence of electron-transport carriers, sites of phosphorylation, membrane orientation, and active transport of metabolites. The chapter reviews number of types of membrane structures and membrane-associated components that have been resolved from whole cells of M . phlei . The different membrane structures appear to contain similar respiratory chains but differ in size and orientation of the membranes. The different types of membrane structures differ in their ability to carry out oxidative phosphorylation or active transport of amino acids. Thus, a meaningful comparison of these membrane-associated processes with the different types of membrane structures is useful in providing some insight concerning the mechanisms of energy transduction underlying these two processes. Protoplast ghosts obtained from M . phlei are about the same size as whole cells, are largely intact, and represent a membrane population that is oriented right-side-out. Sonication of the ghosts or whole cells results in the formation of membrane vesicles, which are referred to as “electron-transport particles” (ETP). The ETP are chiefly oriented inside-out is not a homogeneous population of vesicles because they are contaminated with a small population of membrane vesicles that are oriented right-side-out.

Nitrofurans as electron acceptors for certain respiratory enzymes

Abstract 1. 1. Three isolated respiratory enzymes have been investigated as to their ability to reduce nitrofurans. One of these enzymes diaphorase, a flavoprotein, was found to act as a nitrofuran reductase. Triosephosphate dehydrogenase, a sulfhydryl enzyme; and cytochrome oxidase were not affected by furacin. 2. 2. The inhibition of the reduction of certain hydrogen acceptors (oxygen, methylene blue, and 2,3,5-triphenyltetrazolium) in the presence of furacin can be ascribed to the preferential reduction of furacin by diaphorase.

Studies on the action of nitrofurans on bacterial enzyme systems. III. Furacin interference with dye reductions by Escherichia coli

Abstract The antibacterial nitrofuran, Furacin (5-nitro-2-furaldehyde semicarbazone), was shown to have a marked inhibition on the rate of reduction of methylene blue, Nile blue A, and triphenyltetrazolium chloride by washed Escherichia coli cells in the presence of a variety of substrates. Methylene blue, once reduced, cannot be reoxidized by Furacin, and the inhibition of its reduction has been interpreted as a competition with Furacin for the hydrogen mobilized by the dehydrogenases. The leuco form of Nile blue A can be reoxidized by Furacin, and the complex inhibition of its reduction is an expression of this reoxidation with Furacin acting as a hydrogen acceptor. An interesting interaction of redox indicators was revealed in that indigo carmine can be reduced only through the action of reduced Nile blue A serving as carrier.