Inhibitor energy-transfer

Inhibition of ATP synthase (energy transfer) reduces proton flow from the inter-membrane space to the matrix, which inhibits electron flow in the respiratory chain. Oligomycin, a macrolide antibiotic, prevents phosphoryl group transfer of ATP synthase. Dicyclohexylcarbodimide (DCCD) binds to and inhibits ATP synthase. Similar to the inhibitors of Complexes I, III, and IV, energy transfer inhibitors cause accumulation of reactive electrons and generate ROS. 

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Other work has indicated that chlordane and heptachlor are energy transfer inhibitors as evidenced by marked decreases in oxidative phosphorylation of rat hepatic mitochondria following in vitro incubation of the mitochondria with the pesticides (Ogata et al. 1989). Interestingly, even though heptachlor epoxide is more toxic than either chlordane or heptachlor in tests of general toxicity, it was less effective in inhibiting mitochondrial respiration. 

Figure 1. Representative polarographic traces that depict inhibition by energy transfer inhibitors and allelochemicals of ADP-stimulated electron transport in isolated spinach thylakoids and circumvention of the inhibition by an uncoupler (FCCP, 2 pM). Trace A chlorotributyltin (TBT, 1 pM) trace B phlorizin (400 pM) trace C DCCD (20 pM) trace D quercetin (200 pM) trace E naringenin (1 mM). Water served as electron donor and methyl viologen as electron acceptor. Rates of oxygen utilization, that resulted from the autooxidation of methyl viologen, expressed as pmol 0 consumed/mg Chi h, are indicated parenthet ically.

Herbicides that inhibit the photochemical reactions of isolated chloroplasts have been called routinely inhibitors of the Hill reaction. This has been done primarily for convenience and because, for many years, their action was evaluated under nonphosphorylating conditions, frequently with ferricyanide as the electron acceptor. In the past few years, more sophisticated studies have been conducted with herbicides and more is known about their differential actions. Consequently, Moreland and Hilton (2) separated herbicidal inhibitors of the photochemically induced reactions into the following classes (a) electron transport inhibitors, (b) uncouplers, (c) energy transfer inhibitors,... 

Uncouplers. Uncouplers dissociate electron transport from photophosphorylation. Both noncyclic and cyclic phosphorylation are inhibited, but electron transport reactions are either unaffected or stimulated. Because uncouplers relieve the inhibition of electron transport imposed by energy transfer inhibitors, they are considered to act at a site closer to the electron transport chain than the site of phosphate uptake. In Figure 2, they are shown (site 2) as dissipating some form of conserved energy represented as on the noncyclic and cyclic ATP-gener-ating pathways. Perfluidone is the only herbicide identified to date that functions as a pure uncoupler at pH 8.0 (2). Compounds that uncouple photophosphorylation also uncouple mitochondrial oxidative phosphorylation. 

Energy Transfer Inhibitors. Energy transfer inhibitors act directly on phosphorylation. Like electron transport inhibitors,... 

Fig. 10. Schematic representation of the thyiakoid membrane and various modes of action by uncoupiers, energy-transfer inhibitors, and protonophores.

N Good (1960) Activation of the Hiii reaction by amines. Biochim Biophys Acta 40 502-517 RE McCarty (1980) Deiineation of the mechanism of ATP synthesis in chioropiasts Use of uncoupiers, energy transfer inhibitors, and modifiers of coupiing factor 1. Methods in Enzymology 69 (Photosynthesis and Nitrogen Fixation, Part C (A San Pietro, ed) pp. 719-728... 

Diphenylethers. Different agents can induce peroxidations in photosynthetic membranes. The strongest peroxidative herbicides known are the p-nitrodiphenyl ethers. Although compounds from this group of herbicides can act multifunctionally as electron-transport inhibitors U, 2 ) and energy-transfer inhibitors (1 0), some of them, like oxyfluorfen, exert their dominant phytotoxic action by damaging membrane components. 

Effects of energy transfer inhibitors and coupling efficiency improving agents on ms-DLE and PSP... 

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