Three Classes of Inhibitors Share a Common Binding Domain in Mitochondrial Complex I (NADH:Ubiquinone Oxidoreductase)

Abstract

We have developed two independent methods to measure equilibrium binding of inhibitors to membranebound and partially purified NADH:ubiquinone oxidoreductase (complex I) to characterize the binding sites for the great variety of hydrophobic compounds acting on this large and complicated enzyme. Taking Competition experiments consistently demonstrated that all tested hydrophobic inhibitors of complex I share a common binding domain with partially overlapping sites. Although the rotenone site overlaps with both the piericidin A and the capsaicin site, the latter two sites do not overlap. This is in contrast to the interpretation of enzyme kinetics that have previously been used to define three classes of complex I inhibitors. The existence of only one large inhibitor binding pocket in the hydrophobic part of complex I is discussed in the light of possible mechanisms of proton translocation.

Inhibitors of the Quinone-binding Site Allow Rapid Superoxide Production from Mitochondrial NADH:Ubiquinone Oxidoreductase (Complex I)

“…The simplest explanation of these observations is that there is a particular state of complex I that leads to high superoxide production, and this state can be accessed either during reverse electron transport, or during forward electron transport when an inhibitor occupies the Q-binding site. The fact that different rates of superoxide production were obtained with the three different Q site inhibitors is consistent with the concept of two or three classes of complex I inhibitor with different degrees of overlap in a large Q-binding pocket (25,27). Occupation of one of these binding sites by an inhibitor would trigger superoxide production by promoting the reaction with oxygen of some reductant either within the Q site (such as a semiquinone) or elsewhere within complex I.…”

“…Recent models of complex I propose three different semiquinone sites: two quinone reduction sites and one quinol oxidation site (6,30). Three classes of inhibitor have been described, possibly corresponding to three semiquinone species in a large Q-binding pocket (25,27). Of these species, only SQ Nf exhibits sensitivity to ⌬p.…”

Synthesis and Inhibition Mechanism of Δlac-Acetogenins, a Novel Type of Inhibitor of Bovine Heart Mitochondrial Complex I

“…In particular, the inhibitory potency of compound 7 possessing two n-butyl groups was equivalent to that of bullatacin, one of the most potent inhibitors of bovine complex I (4,6,9). Replacement of the n-butyl group of compound 7 with a bulky tert-butyl group little affected the activity (compound 7 vs 8).…”

Iromycins from Streptomyces sp. and from synthesis: New inhibitors of the mitochondrial electron transport chain

“…Structure elucidation was performed using mass spectrometry and NMR methods, and data were compared to that of iromycin A. The non-natural derivatives iromycin AH (13), AM (14), BM (15), AA (16), and BA (17) were prepared from the microbial metabolites iromycin A (7) and B (8) which can be isolated from Streptomyces sp. Dra 17 in reasonable amounts.…”

“…Yet, the understanding of the competitive behaviour of established complex I inhibitors is hampered by the possibility, that the chemical diverse molecules might either compete for identical binding sites or induce structural dynamic changes in the enzyme which then influence the binding of a second inhibitor. 15,16 Recently, we reported about the isolation and total synthesis of iromycins A-D, a unique family of α-pyridone metabolites from Streptomyces sp. 17,18 The striking structural similarities and clear differences with inhibitors 5 and 6 gave rise to evaluate their inhibitory potential and the site of action within the mitochondrial electron transport chain.…”