NADH Inhibitors - Complex

Espositi, M.D., Ghelli, A., Batta, M., Cortes, D., and Estornell, E. Natural substances (acetogenins) from the family Annonaceae are potent inhibitors of mitochondrial NADH dehydrogenase (complex I). Biochem.., 301, 161, 1994. 

This method was also used with alanine dehydrogenase with NADH as a product inhibitor and substrate inhibition levels of L-alanine (42). At first glance the observed j8 value of 4.9 suggests that a dead-end E-NADH-alanine complex caused the substrate inhibition in an ordered mechanism, however, )8 could not exceed 1.0 unless alanine had as great or greater affinity for E-NADH than its apparent Michaelis constant at low NAD, and, with NAD" present at its (as was the case), the value of j8 could not have exceeded 0.6. The equation for... 

Figure 5 (A) Electrospray mass spectra of (9 mmol r subunit concentration) recombinant Escherichia co//citrate synthase in a bicarbonate buffer at pH 7.5 with 4.5 mmol I nicotinamide adenine dinucleotide (NADH) inhibitor. Dimer and hexamer complexes are evident as are the addition of NADH adducts (1 ) to the hexamer. (Reprinted with permission from Ayed et al. (1998) Rapid Communications in Mass Spectrometry 12 339-344 John Wiley Sons Ltd.) (B) In contrast to A, the spectrum obtained under denaturing conditions (water/methanol 1/1 v/v-i-5% acetic acid, pH 2.5) in which only the monomer in high charge states Is observed. (Additional data for B provided by the authors referred to in A.)...

In mitochondria, the allelochemlcals acted primarily as electron transport inhibitors. Malate oxidation was more sensitive than either succinate or NADH oxidation. No evidence for interaction with a specific membrane complex was obtained. Instead, Inhibition of substrate oxidation seems to result from alterations and perturbations produced in the inner membrane as reflected in interference with the behavior of transport processes. The compounds did not act as uncouplers or directly inhibit ATP synthesis. However, naringenin, some of the flavones, and the cinnamic acids dj inhibit the hydrolysis of ATP catalyzed by mitochondrial Mg -ATPase. 

Table 4.1 Comparative in vitro activity of mitochondrial electron transport (NADH to 2) by complex III inhibitors.

Friedrich, T., VanHeek, P., Leif, H., Ohnishi, T., Forche, E., Kunze, B., Jansen, R., Trowitzsch-Kienast, W., Holfe, G., Reichenbach, H., and Weiss, H. Two binding sites of inhibitors in NADH ubiquinone oxidoreductase (complex I) relationship of one site with the ubiquinone oxido-reductase. Eur. J. Biochem., 219, 691, 1994. 

Reactions of the TCA cycle Enzyme that oxidatively decarboxylates pyruvate, its coenzymes, activators, and inhibitors REACTIONS OF THE TRICARBOXYLIC ACID CYCLE (p. 107) Pyruvate is oxidatively decarboxylated by pyruvate dehydrogenase complex producing acetyl CoA, which is the major fuel for the tricarboxylic acid cycle (TCA cycle). The irreversible set of reactions catalyzed by this enzyme complex requires five coenzymes thiamine pyrophosphate, lipoic acid, coenzyme A (which contains the vitamin pantothenic acid), FAD, and NAD. The reaction is activated by NAD, coenzyme A, and pyruvate, and inhibited by ATP, acetyl CoA, and NADH. 

A crystal structure of a ternary complex of horse liver alcohol dehydrogenase with NADH and the inhibitor, dimethyl sulfoxide, first at 4.5 A resolution1365 and a further refinement to 2.9 A resolution,1366 has been published by Eklund et al. The gross structure of the ternary complex is similar to that of the free enzyme structure. Each subunit is divided into a coenzyme-binding domain and a catalytic domain. The subunits are joined together near the... 

Engler M, Anke T, Sterner O, Brandt U (1997) Pterulinic Acid and Pterulone, Two Novel Inhibitors of NADH Ubiquinone Oxidoreductase (Complex I) Produced by a Pterula Species I. Production, Isolation and Biological Activities. J Antibiot 50 325... 

Two types of inhibitors, pyrazoles and imidazoles (with E-NAD+) and iso-butyramide (with E-NADH), form tight ternary complexes with E-coenzyme, allowing single turnover to be observed (through photometry at 290 nm or fluorescence caused by NADH) and thus titration of the active sites (see Section 9.2.3.). Pyrazole and isobutyramide are kinetically competitive with ethanol and acetaldehyde, respectively. If the reaction E + NADH + aldehyde is run in the presence of a high concentration of pyrazole, the complex E-NAD+ formed by dissociation of alcohol immediately binds pyrazole for a single turnover only. Under favorable conditions, a single NADH oxidation can be observed by stopped-flow techniques to find a kcat of about 150 s 1 and a deuterium isotope effect kD 4 as expected (see Section 9.2.5). 

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