Inhibition electron transport

Rotenone is a complex flavonoid found in the plant Derris ellyptica. It acts by inhibiting electron transport in the mitochondrion. Derris powder is an insecticidal preparation made from the plant, which is highly toxic to hsh. 

Rotenone A complex flavonoid produced by the plant Denis ellyptica. It has insecticidal activity due to its ability to inhibit electron transport in the mitochondrion. 

Allelopathic inhibition of mineral uptake results from alteration of cellular membrane functions in plant roots. Evidence that allelochemicals alter mineral absorption comes from studies showing changes in mineral concentration in plants that were grown in association with other plants, with debris from other plants, with leachates from other plants, or with specific allelochemicals. More conclusive experiments have shown that specific allelochemicals (phenolic acids and flavonoids) inhibit mineral absorption by excised plant roots. The physiological mechanism of action of these allelochemicals involves the disruption of normal membrane functions in plant cells. These allelochemicals can depolarize the electrical potential difference across membranes, a primary driving force for active absorption of mineral ions. Allelochemicals can also decrease the ATP content of cells by inhibiting electron transport and oxidative phosphorylation, which are two functions of mitochondrial membranes. In addition, allelochemicals can alter the permeability of membranes to mineral ions. Thus, lipophilic allelochemicals can alter mineral absorption by several mechanisms as the chemicals partition into or move through cellular membranes. Which mechanism predominates may depend upon the particular allelochemical, its concentration, and environmental conditions (especially pH). 

Mechanism of Action. Atovaquone appears to selectively inhibit electron transport in susceptible microorganisms.6 This inhibition directly decreases production of ATP in the microorganism and may interfere with nucleic acid synthesis, ultimately resulting in death of the parasite. 

Mechanism of Action. Nitazoxanide appears to inhibit electron transport in susceptible protozoa, thus... 

Rotenone and amytal inhibit electron transport at NADH dehydrogenase, antimycin A inhibits the cytochrome bci complex, and cyanide (CN ), azide (N3 ) and carbon monoxide (CO) all inhibit cytochrome oxidase. 

Note A problem in the interpretation of the amiloride inhibition of proton release is the amiloride inhibition of di-ferric transferrin and ferricyanide reduction (Sun et al., 1987). The question arises does inhibition of the exchanger inhibit electron transport or does inhibition of electron transport inhibit a H release not dependent on the exchanger Exchanger inhibition is most likely because of the Na+ dependence for part of the H release (Sun et al., 1988). As an alternative, proton transport may be necessary for electron transport (Stahl and Anst, 1993). 

One example is provided by the optical isomers of l-(a-methyl-benzy])-3-(3,4-dichlorophenyl)urea (17). This chemical is an inhibitory uncoupler. The S-isomer inhibits electron transport, but the R-isomer is noninhibitory. The inactive isomer does not compete with the active isomer at the photosystem II site. The phosphorylation site shows no optical specificity. The two isomers do not differ significantly in their lipophilicity. 

Table 17.1 Compounds Inhibiting Electron Transport and ADP Phosphorylation by Mitochondria...

The absence of ADP is acting, in effect, as an inhibitor of electron transport, for reasons discussed in Prob. 14.6 below. Hence, by application of the crossover theorem (Chap. 10), there are large differences in the reduction of sites of the electron-transport-chain between NAD and coenzyme Q, between cytochrome b and cytochrome c, and between cytochrome c and cytochrome a. Therefore, the absence of ADP must be inhibiting electron transport at these points in fact, these are the sites of proton extrusion leading to ATP synthesis during electron transport. 

Palmer et al. (91) have suggested that in addition to the above site, rotenone and piericidin A also inhibit electron transport immediately on the substrate side of cytochrome Ci. This view has not been accepted by others. Teeter et al. (9 ) have shown that secondary effects of rotenone and piericidin can be observed at other regions of the respiratory chain when high concentrations of the inhibitors are used, as by necessity did Palmer et al. in their EPR experiments. 

In H. salinarium (cutinibnim), NADH is oxidized through c-type cytochromes and an cytochrome a oxidase. 2-heptyl-4-hydroxyquinoline-yV-oxide (HOQNO) inhibits electron transport chain at the level of the NADH dehydrogenase. The salt dependence of the NADH oxidase system indicates that the salt dependence of the NADH oxidase system is a reflection of the sensitivity of the NAD dehydrogenase [95]. 

Structure of antimycin A, an antibiotic that inhibits electron transport from CoQ to cytochrome c. 

The mode of action studies suggest that nitro-diphenyl ethers act on the photosynthetic systems of plants. Two pathways are involved, one requiring light, the other not. Thus they can inhibit noncyclic electron transport and coupled photophosphorylation in chloroplasts, and in mitochondria they inhibit electron transport. (Matsunaka, 1969a, 1969b and Moreland et al.. 1970). 

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