The interaction of yeast Complex III with some respiratory inhibitors

Inhibitory Analogs of Ubiquinol Act Anti-cooperatively on the Yeast Cytochrome bc1 Complex

“…From titrating the inhibitor with 2.5 nM or 1.5 M bc 1 complex, it is clear that the stoichiometry for inhibition of the yeast bc 1 complex by antimycin is one inhibitor per enzyme monomer. This agrees with previous results for titration of the yeast enzyme with this inhibitor (16).…”

Evidence for a unique Rieske iron‐sulphur centre in Heliobacterium chlorum

“…UHDBT ( fig.4c) and stigmatellin ( fig.4d) shift the g,-line to higher field values, just as has been reported for the Rieske centres from mitochondria [20,21] and plants [22,23]. However, in H. chlorum both these inhibitors induce a shift of the g,-trough to lower field position, whereas the opposite effect is usually observed both in cytochrome bcl [20,21] and b4f complexes (Nitschke, unpublished). Thus, the effects of the Qo-site inhibitors on the EPR spectrum of the centre are comparable but not identical with what has been reported for other Rieske proteins.…”

Mitochondrial cytochrome b: evolution and structure of the protein

“…The techniques of sequence analysis that have been discussed thus far are of limited value for understandlng the details of the redox functton of cytochrome b since no atomic structure is available, although crystallzation of the beef bc I complex has been reported [110,111] Complementary mformatlon is indispensable for refinements of the present models of mltochondrlal cytochrome b structure This mformation is also important for understanding the functton of structural features that are conserved [8,18,19,65,68] Important relationships can be estabhshed indirectly between the structural features of cytochrome b and the sensitivity of the bc I complex to its lnhlbltors [5,6,8,9,12,19,[24][25][26][27][28]36,39,44,46,68,73,80,81,90] T h i s IS possible because the inhlbitors of the b c 1 complex bind directly to cytochrome b as evidenced by photoafflmty labeling [17], changes in spectroscopic properties [80,81,[112][113][114][115] and genetic analysis [4][5][6]19,24,26,36,68,…”

“…A large variety of compounds act as center o inhibltors (see [113] for a review) Although they all block reduction of the 'Rleske' Iron-sulphur protein and prevent cytochrome b reduction in the presence of antlmycln [9,15,80,94,106,[112][113][114][115], they can be subdivided into three types depending upon their effect on the metal groups at center o [113] The methoxyacrylates, including myxothlazol, do not substantially alter the mid-point potential or the EPR line shape of the Rieske Iron-sulphur cluster, but alter the electronic absorption spectra of the cytochrome b hemes [80,81,[113][114][115] The hydroxyquinones, such as UHDBT, specifically alter the cluster and its redox equilibrium with cytochrome c 1 and ublqulnol [9,73,81,113,114] The chromone inhlbitors, including stigmatelhn, alter both the E P R spectra and the midpoint potential of the Iron-sulphur cluster, and the optical spectra of the cytochrome b hemes (Refs 81, 113, 126 and references therein) The latter are universal center o lnhlbltors, since they are potent lnhlbltors of the the bf complex [12,121] as well as of the QB site in photosynthetic reaction centers [121,123] A detailed characterization of mutants resistant towards center o lnhibltors is available from studies of both mitochondrlal [36,134,137,138] and bacterial systems [8,19.44,68,69,73,81] (Table IV) The results indicate that different positions within the cytochrome b protein are critical for the binding of myxothlazol and stigmatelhn Apparently, chloroplast bf complex is insensitive to myxothlazol but quite sensitive to stigmatelhn [3,121] This can be correlated with the fact that some mutations affecting myxothlazol sensitiv...…”

“…Correlations between an unusual response to one bc 1 inhibitor and the sequence of the cytochrome b protein are most convincing when they combine sequence analysis in related s p e o e s with the information derived from mutants In the case of the natural resistance of fish to fumculosln [90], the results of a selected screening of fumculosin sensitivity m animal m l t o c h o n d n a suggested that the substitution of the conserved alanme 126 with the bulky m e t h l o n m e in the fish protein (Fig 1) is probably responsible for a substantial increase m the tltre of this inhibitor relatwe to normally sensltwe s p e o e s (Table V and R e f 90) Natural resistance in the plant mItochondnal bc t complex [142] could also be correlated with the exchange of A126 with the bulkier V m the cytochrome b sequence (Fig 2 and R e f 90) The buried location of position 126 within the transmembrane sector of hehx C (Fig 1) may account for the 'hybrid' effects of fumculosln, which effects both center i and center o [90,114,[143][144][145][146] Note that the proteins having a bulky amino a o d at poslt~on 126 also show resistance to U H D B T (Table V), which xs a center o inhibitor that shares with funlculosm the property of effectlng both qulnone sites [113,114,143,144] An interesting property of funlculosln is its remarkable species specificity, even among mammals [143,147] The volume pattern and the comparison of the sequences of sensltwe and resistant species suggested previously that position 194 may also be revolved in funlculosln binding [90] By inspecting the aligned sequences, we noticed that the rabbit protein shows the substitution of alanine 194 with a bulkier vahne residue (Fig 1) Hence, rabbit mltochondrla were expected to be quite resistant to funlculosin, which would explain why rabbits are resistant to this drug in vwo [147] This ~s indeed the case, since the inhibitory potency of funlculosln on the ublqumol cytochrome c reductase actwlty is about 60-fold lower for m l t o c h o n d n a ~solated from rabbit than those from sensltwe mammals (Table V) The cytochrome b proteins of zebra and donkey also have vahne at position 194 (Fig 1 and R e f 32) and differ from that of pig, a...…”