Gramicidin uncoupling

Dinitrophenol and gramicidin, uncouplers of the oxidative phospho-r>lation in mitochondria, also suppressed the respiration in propionibacteria. Especially sensitive to the action of imcouplers were cells of P. petersonii, in which the respiration was completely blocked by gramicidin at 10 p g/ml, while in P. shermanii it was inhibited by 93% at 100 iig/ml gramicidin. Dinitrophenol at a concentration of MO" M decreased the rate of respiration by 40% in P. shermanii, but blocked it completely in P. petersonii. 

Gramicidin was found to uncouple the phosphorylation of ADP from the enzymatic reduction of ferricytochrome C167,168,169,170,171,172,173,174,175 ... 

A group of antibiotics (e.g., valinomycin, nigericin, and gramicidin A) transport cations across the cell membrane. Such agents, known as ionophores, are widely used to probe membrane structure and function. Ionophores uncouple oxidative phosphorylation. Valinomycin, a cyclic peptide (Figure 14-17), forms a lipid-soluble complex with K+ that readily passes through the inner membrane, whereas K+ by itself does not. In the valinomycin-K complex, hydrophobic groups, present on the outside, facilitate transport of the complex in the lipid environment ... 

Compounds known as imcouplers inhibit the phosphorylation of ADP without affecting electron transport. A well-known example of an uncoupler is 2,4-dinitwphenol. Various antibiotics, such as valinomycin and gramicidin A,... 

FIGURE 20.14 Some uncouplers of oxidative phosphorylation 2,4-dinitrophenol, valinomycin, and gramicidin A. 

Various chemicals cause uncoupling by increasing the permeability of the membrane to protons and other small ions. Detergents, which destabilize the membrane structure, can have this effect [15]. Several small molecules, including some classical uncouplers, have been described as affecting the membrane permeability transition (MPT), which causes a dramatic increase in the ability of ions to move across the membrane [9, 16, 17]. More specific effects that increase the permeability of the membrane to protons, as caused by the peptide gramicidin A, also lead to uncoupling [14, 18, 19]. 

H/e ratio in dependence on the e-flow increase induced by addition of the uncoupling agents nigericin, FCCP, and gramicidin for actinic light of 100 Wm-2 intensity. 

The oxidative phosphorylation by the respiratory chains of P. shermanii and P. petersonii is sensitive to uncouplers and inhibitors 2,4-DNP (110 M) reduced the P/NADH ratio in both cultures by 20-40% gramicidin (1 10 M) by 60% o-phenanthroline (110 M) by 20% in P. shermanii and by 80% in P. petersonii. A marked inhibition of the oxidative phosphorylation by the iron chelator o-phenanthroline in P. petersonii as compared with P. shermanii may indicate an essential role of non-heme iron in the oxidative phosphorylation of the former. Pretreatment of the particulate fraction of propionibacterial cells by UV-light led to a decrease in P/NADH ratio by... 

A similar conclusion follows from the work of de Kouchkovsky s group who measured the rate of ATP formation driven by a cyclic (PSl) or non-cyclic (PSl -h PS2) electron transport chain as a function of the apparent ApH value [99]. The hypothesis of the direct interaction of PS2 protonic domains with ATPsynthase was also considered by Yaguzhinsky s group [124] who studied the effects of the uncoupler gramicidin D on the photophosphorylation rate in chloroplasts during cyclic or noncyclic electron transport. 

Mitochondrial studies have uncovered a whole group of substances, e.g., 2,4-dinitrophenol, gramicidin, and aureomycin, which can dissociate esterification of inorganic phosphate from the oxidation process. These substances have become known as uncoupling agents. There is some evidence that they uncouple by dephosphorylating the primary acceptor complex before the phosphoryl group can be transferred to ADP. ... 

Substances such as 2,4-dinitrophenol, azide, gramicidin, and arsenite, which uncouple phosphorylation from oxidation, inhibit the oxidation of fatty acidsbut not of the primer itself. Lehninger and his co-workers showed that the oxidation of the reduced form of the codehydrogenase, DPNH or reduced DPN, caused oxidative phosphorylation. Thus, the oxidation of a tricarboxylic acid intermediate was not obligatory for fatty acid activation. As might be expected, therefore, fatty acid breakdown was initiated by the oxidation of DPNH in the absence of tricarboxlic acid cycle intermediates. The absence of tricarboxylic acid cycle inter-... 

A number of other uncouplers like FCCP, DNP, gramicidin or valinomycin was tested but failed to show comparable effects. Also combinations of FCCP and valinomycin (that should mimic nigericin-induced exchange) did not induce... 

Fig 2). This correlation was no longer found when the effect of different gramicidin concentrations were tested (Fig. 3). Uncoupling by increasing gramicidin concentrations resulted in decreasing apparent K-values. 

---