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W1968155346 abstract "Eight synthetic analogues of tentoxin (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZPhe3-Gly4)) modified in residues 1, 2, and 3 were checked for their ability to inhibit and reactivate the ATPase activity of the activated soluble part of chloroplast ATP synthase. The data were consistent with a model involving two binding sites of different affinities for the toxins. The occupancy of the high affinity site (or tight site) gave rise to an inactive complex, whereas filling both sites (tight + loose) gave rise to a complex of variable activity, dependent on the toxin analogue. Competition experiments between tentoxin and nonreactivating analogues allowed discrimination between the absence of binding and a nonproductive binding to the site of lower affinity (or loose site). The affinity for the loose site was not affected significantly by the modifications of the tentoxin molecule, whereas the affinity for the tight site was found notably changed. Increasing the size of side chain 1 or 2 and introducing a net electrical charge both resulted in a decrease of affinity for the tight site, but the second change dominated the first one. The activity of different ternary complexes enzyme-tentoxin-analogue depended on the nature of the toxin bound on each site and not only on that bound on the loose site. This demonstrates that the reactivation process results from an interaction, direct or not, between these two binding sites. Possible molecular mechanisms are discussed. Eight synthetic analogues of tentoxin (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZPhe3-Gly4)) modified in residues 1, 2, and 3 were checked for their ability to inhibit and reactivate the ATPase activity of the activated soluble part of chloroplast ATP synthase. The data were consistent with a model involving two binding sites of different affinities for the toxins. The occupancy of the high affinity site (or tight site) gave rise to an inactive complex, whereas filling both sites (tight + loose) gave rise to a complex of variable activity, dependent on the toxin analogue. Competition experiments between tentoxin and nonreactivating analogues allowed discrimination between the absence of binding and a nonproductive binding to the site of lower affinity (or loose site). The affinity for the loose site was not affected significantly by the modifications of the tentoxin molecule, whereas the affinity for the tight site was found notably changed. Increasing the size of side chain 1 or 2 and introducing a net electrical charge both resulted in a decrease of affinity for the tight site, but the second change dominated the first one. The activity of different ternary complexes enzyme-tentoxin-analogue depended on the nature of the toxin bound on each site and not only on that bound on the loose site. This demonstrates that the reactivation process results from an interaction, direct or not, between these two binding sites. Possible molecular mechanisms are discussed. F0F1 proton ATPases (or ATP synthases) are bound to energy-transducing membranes and couple the phosphorylation of ADP into ATP to the dissipation of a protonmotive force. They consist of a transmembrane proton channel (F0) and an extrinsic part (F1) bearing six nucleotide binding sites, catalytic and noncatalytic. The F1 moiety is composed of five different subunits named α, β, γ, δ, and ε (stoichiometry α[3] β[3] γ[1] δ[1] ε[1]). Subunits α and β bear the nucleotide binding sites and are disposed as a crown, the γ subunit being located in the center of this structure (1Boekema E.J. Berden J.A. van Heel M.G. Biochim. Biophys. Acta. 1986; 851: 353-360Crossref PubMed Scopus (103) Google Scholar, 2Yoshimura H. Matsumoto M. Endo S. Nagayama K. Ultramicroscopy. 1990; 32: 265-274Crossref Scopus (97) Google Scholar, 3Boekema E.J. Xiao J. McCarty R.E. Biochim. Biophys. Acta. 1990; 1020: 49-56Crossref Scopus (24) Google Scholar, 4Abrahams J.P. Leslie A.G.W. Lutter R. Walker J.E. Nature. 1994; 37: 621-628Crossref Scopus (2734) Google Scholar). The F0 moiety basically consists of three or four different subunits (Escherichia coli: a[1] b[2] c[9–12]; chloroplast: a[1] b[1] b′[1] c[9–12]), the mitochondrial enzyme having additional subunits (5Collinson I.R. Runswick M.J. Buchanan S.K. Fearnley I.M. Skehel J.M. van Raaij M.J. Griffiths D.E. Walker J.E. Biochemistry. 1994; 33: 7971-7978Crossref PubMed Scopus (162) Google Scholar, 6Arselin G. Vaillier J. Graves P.-V. Velours J. J. Biol. Chem. 1996; 271: 20284-20290Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). It is proposed that the F0 moiety would work as a rotative proton-driven motor, the rotor consisting of the c subunits (7Vik S.B. Antonio B.J. J. Biol. Chem. 1994; 269: 30364-30369Abstract Full Text PDF PubMed Google Scholar), presumably arranged in a crown (8Singh S. Turina P. Bustamante C.J. Keller D.J. Capaldi R. FEBS Lett. 1996; 397: 30-34Crossref PubMed Scopus (105) Google Scholar). The rotation would be transmitted to the γ subunit of the F1 moiety (9Duncan T.M. Bulygin V.V. Zhou Y. Hutcheon M.L. Cross R.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 10964-10968Crossref PubMed Scopus (458) Google Scholar), which should modify sequentially the three catalytic sites located on β subunits (4Abrahams J.P. Leslie A.G.W. Lutter R. Walker J.E. Nature. 1994; 37: 621-628Crossref Scopus (2734) Google Scholar) to induce ATP synthesis (10Boyer P.D. Biochim. Biophys. Acta. 1993; 1140: 215-250Crossref PubMed Scopus (913) Google Scholar). Experimental arguments have been presented against (11Wang J.H. Cesana J. Wu J.C. Biochemistry. 1987; 26: 5527-5533Crossref PubMed Scopus (8) Google Scholar, 12Musier K.M. Hammes G.G. Biochemistry. 1987; 26: 5982-5988Crossref PubMed Scopus (23) Google Scholar) and for (9Duncan T.M. Bulygin V.V. Zhou Y. Hutcheon M.L. Cross R.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 10964-10968Crossref PubMed Scopus (458) Google Scholar, 13Aggeler R. Haughton M.A. Capaldi R.A. J. Biol. Chem. 1995; 270: 9185-9191Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar, 14Sabbert D. Engelbrecht S. Junge W. Nature. 1996; 381: 623-625Crossref PubMed Scopus (461) Google Scholar, 15Noji H. Yasuda R. Yoshida M. Kinosia K. Nature. 1997; 386: 299-302Crossref PubMed Scopus (1940) Google Scholar) the rotation of γ. An essential feature of this model is that the cooperative functioning among the three catalytic sites is strictly related to the rotation of the γ subunit and thus to the proton pumping activity.Tentoxin (TTX) 1The abbreviations used are: TTX, tentoxin or (cyclo-(l-N-MeAla1-l-Leu2-N-MeΔZPhe3-Gly4)); CF1, chloroplast F1 H+-ATPase; CF1-ε, chloroplast F1 H+-ATPase devoid of ε subunit; FTIR, Fourier transformation infrared spectroscopy; Lys2-TTX, (cyclo-(l-N-MeAla1-l-Lys2-N-MeΔZPhe3-Gly4)); Lys(Z)2-TTX, (cyclo-(l-N-MeAla1-l-Lys(Z)2-N-MeΔZPhe3-Gly4));MeGlu1-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZPhe3-Gly4)); MeGlu(tBu)1-TTX, (cyclo-(l-N-MeGlu(tBu)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer1-TTX, (cyclo-(l-N-MeSer1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer(Bn)1-TTX, (cyclo-(l-N-MeSer(Bn)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeΔzPhe or ΔPhe, α,β-dehydrophenylalanineN-methylated in Z configuration; Tyr3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr3-Gly4)); Tyr(Me)3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr(Me)3-Gly4)); Tricine, N-[2-hydroxy-1,1-bis(hydroxy- methyl)ethyl]glycine. 1The abbreviations used are: TTX, tentoxin or (cyclo-(l-N-MeAla1-l-Leu2-N-MeΔZPhe3-Gly4)); CF1, chloroplast F1 H+-ATPase; CF1-ε, chloroplast F1 H+-ATPase devoid of ε subunit; FTIR, Fourier transformation infrared spectroscopy; Lys2-TTX, (cyclo-(l-N-MeAla1-l-Lys2-N-MeΔZPhe3-Gly4)); Lys(Z)2-TTX, (cyclo-(l-N-MeAla1-l-Lys(Z)2-N-MeΔZPhe3-Gly4));MeGlu1-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZPhe3-Gly4)); MeGlu(tBu)1-TTX, (cyclo-(l-N-MeGlu(tBu)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer1-TTX, (cyclo-(l-N-MeSer1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer(Bn)1-TTX, (cyclo-(l-N-MeSer(Bn)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeΔzPhe or ΔPhe, α,β-dehydrophenylalanineN-methylated in Z configuration; Tyr3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr3-Gly4)); Tyr(Me)3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr(Me)3-Gly4)); Tricine, N-[2-hydroxy-1,1-bis(hydroxy- methyl)ethyl]glycine. is a natural cyclic tetrapeptide (cyclo-(L-MeAla1-L-Leu2-MeΔZPhe3-Gly4)), produced by several phytopathogenic fungi of the Alternariagenus (16Meyer W.L. Templeton G.E. Grable C.T. Sigel C.W. Jones R. Woodhead S.H. Sauer C. Tetrahedron Lett. 1971; 25: 2357-2360Crossref Scopus (40) Google Scholar, 17Liebermann B. Oertel B. Z. Allg. Mikrobiol. 1983; 23: 503-511Crossref Google Scholar). Under special conditions, this toxin induces a chlorosis in some higher plants (18Durbin R.D. Uchytil T.F. Phytopathology. 1977; 67: 602-603Crossref Google Scholar). It specifically inhibits ATP synthesis in isolated chloroplasts (19Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 2245-2248Crossref PubMed Scopus (131) Google Scholar). In vitro and at low concentrations (10−8–10−7m), TTX inhibits the isolated chloroplast F1-ATPase (19Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 2245-2248Crossref PubMed Scopus (131) Google Scholar, 20Steele J.A. Durbin R.D. Uchytil T.F. Rich D.H. Biochim. Biophys. Acta. 1978; 501: 72-82Crossref PubMed Scopus (49) Google Scholar, 21Steele J.A. Uchytil T.F. Durbin R.D. Biochim. Biophys. Acta. 1978; 504: 136-141Crossref PubMed Scopus (44) Google Scholar, 22Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Biochem. Biophys. Res. Commun. 1978; 84: 215-218Crossref PubMed Scopus (8) Google Scholar), but at higher concentrations (10−5–10−4m), it strongly stimulates ATPase activity (21Steele J.A. Uchytil T.F. Durbin R.D. Biochim. Biophys. Acta. 1978; 504: 136-141Crossref PubMed Scopus (44) Google Scholar, 22Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Biochem. Biophys. Res. Commun. 1978; 84: 215-218Crossref PubMed Scopus (8) Google Scholar, 23Dahse I. Pezennec S. Girault D. Berger G. André F. Liebermann B. J. Plant Physiol. 1994; 143: 615-620Crossref Scopus (21) Google Scholar). At these same concentrations, the effect observed on membrane-bound ATPase (F0F1 complex) is restricted to a partial release of inhibition, but the reactivated F0F1complex recovers the ability to couple proton transport to ATP synthesis (24Sigalat C. Pitard B. Haraux F. FEBS Lett. 1995; 368: 253-256Crossref PubMed Scopus (15) Google Scholar). TTX dramatically disturbs the interactions among different nucleotide sites of ATPase, whatever the toxin concentration range (25Fromme P. Dahse I. Gräber P. Z. Naturforsch. 1992; 47c: 239-244Google Scholar, 26Hu N. Mills D.A. Huchzermeyer B. Richter M.L. J. Biol. Chem. 1993; 268: 8536-8540Abstract Full Text PDF PubMed Google Scholar). Simultaneous perturbation of these interactions and preservation of proton coupling in the TTX-reactivated form are intriguing in the context of rotational catalysis. Understanding the inhibitory and reactivating properties of TTX is therefore one of the elements that may contribute to the elucidation of the mechanism of energy coupling.It has been demonstrated (27Pinet E. Gomis J.-M. Girault G. Cavelier F. Verducci J. Noël J.-P. André F. FEBS Lett. 1996; 395: 217-220Crossref PubMed Scopus (17) Google Scholar) that CF1 binds two molecules of TTX on two sites of different affinities, which could be related to the inhibitory and reactivating effects of this molecule. These binding sites have not yet been identified, and the reasons for the specificity of TTX for the CF1-ATP synthase of some higher plants remain obscure (23Dahse I. Pezennec S. Girault D. Berger G. André F. Liebermann B. J. Plant Physiol. 1994; 143: 615-620Crossref Scopus (21) Google Scholar, 28Avni A. Anderson J.D. Holland N. Rochaix J.-D. Gromet-Elhanan Z. Edelman M. Science. 1992; 257: 1245-1247Crossref PubMed Scopus (59) Google Scholar). TTX stabilizes and enhances the ATPase activity of an α3β3 complex from spinach CF1 (29Sokolov M. Gromet-Elhanan Z. Biochemistry. 1996; 35: 1242-1248Crossref PubMed Scopus (23) Google Scholar), which proves that the γ, δ, ε subunits are not required for the stimulation effect of TTX but suggests that they could be necessary for the inhibition.We have shown recently (30Pinet E. Cavelier F. Verducci J. Girault G. Dubart L. Haraux F. Sigalat C. André F. Biochemistry. 1996; 35: 12804-12811Crossref PubMed Scopus (20) Google Scholar) that a very limited change in the molecule of TTX (replacement of l-MeAla1 byl-MeSer1) resulted in a dramatic loss of the reactivating effect at high concentrations, although the inhibitory effect at lower concentrations was unaffected. This led to the idea that it was possible to discriminate inhibitory and activating effects by an appropriate set of molecules derived from TTX. Because high concentrations of MeSer1-TTX were able to prevent CF1-ATPase reactivation by high concentrations of TTX, we proposed that MeSer1-TTX could bind the reactivating site competitively with TTX, giving rise to a poorly active form of the enzyme. However, it cannot be excluded that MeSer1-TTX prevents reactivation simply by chasing TTX from the high affinity site. The question was whether the stimulation by TTX only involves the low affinity binding site or the two binding sites of CF1. To get information about possible cooperation among TTX binding sites, we have used a kinetic approach consisting of studying the catalytic properties of ternary complexes formed by CF1-ε and different TTX analogues. This approach involves various combinations of analogues of different affinities for the inhibitory site and able or not to reactivate the enzyme at high concentrations. The results suggested that both binding sites participate in the formation of the reactivated state. At the same time, we were able to characterize the binding and effector properties of the set of TTX analogues modified in various positions. This allowed us to make hypotheses about the domains of the TTX molecule which are important for binding, inhibition, and stimulation. F0F1 proton ATPases (or ATP synthases) are bound to energy-transducing membranes and couple the phosphorylation of ADP into ATP to the dissipation of a protonmotive force. They consist of a transmembrane proton channel (F0) and an extrinsic part (F1) bearing six nucleotide binding sites, catalytic and noncatalytic. The F1 moiety is composed of five different subunits named α, β, γ, δ, and ε (stoichiometry α[3] β[3] γ[1] δ[1] ε[1]). Subunits α and β bear the nucleotide binding sites and are disposed as a crown, the γ subunit being located in the center of this structure (1Boekema E.J. Berden J.A. van Heel M.G. Biochim. Biophys. Acta. 1986; 851: 353-360Crossref PubMed Scopus (103) Google Scholar, 2Yoshimura H. Matsumoto M. Endo S. Nagayama K. Ultramicroscopy. 1990; 32: 265-274Crossref Scopus (97) Google Scholar, 3Boekema E.J. Xiao J. McCarty R.E. Biochim. Biophys. Acta. 1990; 1020: 49-56Crossref Scopus (24) Google Scholar, 4Abrahams J.P. Leslie A.G.W. Lutter R. Walker J.E. Nature. 1994; 37: 621-628Crossref Scopus (2734) Google Scholar). The F0 moiety basically consists of three or four different subunits (Escherichia coli: a[1] b[2] c[9–12]; chloroplast: a[1] b[1] b′[1] c[9–12]), the mitochondrial enzyme having additional subunits (5Collinson I.R. Runswick M.J. Buchanan S.K. Fearnley I.M. Skehel J.M. van Raaij M.J. Griffiths D.E. Walker J.E. Biochemistry. 1994; 33: 7971-7978Crossref PubMed Scopus (162) Google Scholar, 6Arselin G. Vaillier J. Graves P.-V. Velours J. J. Biol. Chem. 1996; 271: 20284-20290Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). It is proposed that the F0 moiety would work as a rotative proton-driven motor, the rotor consisting of the c subunits (7Vik S.B. Antonio B.J. J. Biol. Chem. 1994; 269: 30364-30369Abstract Full Text PDF PubMed Google Scholar), presumably arranged in a crown (8Singh S. Turina P. Bustamante C.J. Keller D.J. Capaldi R. FEBS Lett. 1996; 397: 30-34Crossref PubMed Scopus (105) Google Scholar). The rotation would be transmitted to the γ subunit of the F1 moiety (9Duncan T.M. Bulygin V.V. Zhou Y. Hutcheon M.L. Cross R.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 10964-10968Crossref PubMed Scopus (458) Google Scholar), which should modify sequentially the three catalytic sites located on β subunits (4Abrahams J.P. Leslie A.G.W. Lutter R. Walker J.E. Nature. 1994; 37: 621-628Crossref Scopus (2734) Google Scholar) to induce ATP synthesis (10Boyer P.D. Biochim. Biophys. Acta. 1993; 1140: 215-250Crossref PubMed Scopus (913) Google Scholar). Experimental arguments have been presented against (11Wang J.H. Cesana J. Wu J.C. Biochemistry. 1987; 26: 5527-5533Crossref PubMed Scopus (8) Google Scholar, 12Musier K.M. Hammes G.G. Biochemistry. 1987; 26: 5982-5988Crossref PubMed Scopus (23) Google Scholar) and for (9Duncan T.M. Bulygin V.V. Zhou Y. Hutcheon M.L. Cross R.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 10964-10968Crossref PubMed Scopus (458) Google Scholar, 13Aggeler R. Haughton M.A. Capaldi R.A. J. Biol. Chem. 1995; 270: 9185-9191Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar, 14Sabbert D. Engelbrecht S. Junge W. Nature. 1996; 381: 623-625Crossref PubMed Scopus (461) Google Scholar, 15Noji H. Yasuda R. Yoshida M. Kinosia K. Nature. 1997; 386: 299-302Crossref PubMed Scopus (1940) Google Scholar) the rotation of γ. An essential feature of this model is that the cooperative functioning among the three catalytic sites is strictly related to the rotation of the γ subunit and thus to the proton pumping activity. Tentoxin (TTX) 1The abbreviations used are: TTX, tentoxin or (cyclo-(l-N-MeAla1-l-Leu2-N-MeΔZPhe3-Gly4)); CF1, chloroplast F1 H+-ATPase; CF1-ε, chloroplast F1 H+-ATPase devoid of ε subunit; FTIR, Fourier transformation infrared spectroscopy; Lys2-TTX, (cyclo-(l-N-MeAla1-l-Lys2-N-MeΔZPhe3-Gly4)); Lys(Z)2-TTX, (cyclo-(l-N-MeAla1-l-Lys(Z)2-N-MeΔZPhe3-Gly4));MeGlu1-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZPhe3-Gly4)); MeGlu(tBu)1-TTX, (cyclo-(l-N-MeGlu(tBu)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer1-TTX, (cyclo-(l-N-MeSer1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer(Bn)1-TTX, (cyclo-(l-N-MeSer(Bn)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeΔzPhe or ΔPhe, α,β-dehydrophenylalanineN-methylated in Z configuration; Tyr3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr3-Gly4)); Tyr(Me)3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr(Me)3-Gly4)); Tricine, N-[2-hydroxy-1,1-bis(hydroxy- methyl)ethyl]glycine. 1The abbreviations used are: TTX, tentoxin or (cyclo-(l-N-MeAla1-l-Leu2-N-MeΔZPhe3-Gly4)); CF1, chloroplast F1 H+-ATPase; CF1-ε, chloroplast F1 H+-ATPase devoid of ε subunit; FTIR, Fourier transformation infrared spectroscopy; Lys2-TTX, (cyclo-(l-N-MeAla1-l-Lys2-N-MeΔZPhe3-Gly4)); Lys(Z)2-TTX, (cyclo-(l-N-MeAla1-l-Lys(Z)2-N-MeΔZPhe3-Gly4));MeGlu1-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZPhe3-Gly4)); MeGlu(tBu)1-TTX, (cyclo-(l-N-MeGlu(tBu)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer1-TTX, (cyclo-(l-N-MeSer1-l-Leu2-N-MeΔZPhe3-Gly4)); MeSer(Bn)1-TTX, (cyclo-(l-N-MeSer(Bn)1-l-Leu2-N-MeΔZPhe3-Gly4)); MeΔzPhe or ΔPhe, α,β-dehydrophenylalanineN-methylated in Z configuration; Tyr3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr3-Gly4)); Tyr(Me)3-TTX, (cyclo-(l-N-MeGlu1-l-Leu2-N-MeΔZTyr(Me)3-Gly4)); Tricine, N-[2-hydroxy-1,1-bis(hydroxy- methyl)ethyl]glycine. is a natural cyclic tetrapeptide (cyclo-(L-MeAla1-L-Leu2-MeΔZPhe3-Gly4)), produced by several phytopathogenic fungi of the Alternariagenus (16Meyer W.L. Templeton G.E. Grable C.T. Sigel C.W. Jones R. Woodhead S.H. Sauer C. Tetrahedron Lett. 1971; 25: 2357-2360Crossref Scopus (40) Google Scholar, 17Liebermann B. Oertel B. Z. Allg. Mikrobiol. 1983; 23: 503-511Crossref Google Scholar). Under special conditions, this toxin induces a chlorosis in some higher plants (18Durbin R.D. Uchytil T.F. Phytopathology. 1977; 67: 602-603Crossref Google Scholar). It specifically inhibits ATP synthesis in isolated chloroplasts (19Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 2245-2248Crossref PubMed Scopus (131) Google Scholar). In vitro and at low concentrations (10−8–10−7m), TTX inhibits the isolated chloroplast F1-ATPase (19Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 2245-2248Crossref PubMed Scopus (131) Google Scholar, 20Steele J.A. Durbin R.D. Uchytil T.F. Rich D.H. Biochim. Biophys. Acta. 1978; 501: 72-82Crossref PubMed Scopus (49) Google Scholar, 21Steele J.A. Uchytil T.F. Durbin R.D. Biochim. Biophys. Acta. 1978; 504: 136-141Crossref PubMed Scopus (44) Google Scholar, 22Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Biochem. Biophys. Res. Commun. 1978; 84: 215-218Crossref PubMed Scopus (8) Google Scholar), but at higher concentrations (10−5–10−4m), it strongly stimulates ATPase activity (21Steele J.A. Uchytil T.F. Durbin R.D. Biochim. Biophys. Acta. 1978; 504: 136-141Crossref PubMed Scopus (44) Google Scholar, 22Steele J.A. Uchytil T.F. Durbin R.D. Bhatnagar P.K. Rich D.H. Biochem. Biophys. Res. Commun. 1978; 84: 215-218Crossref PubMed Scopus (8) Google Scholar, 23Dahse I. Pezennec S. Girault D. Berger G. André F. Liebermann B. J. Plant Physiol. 1994; 143: 615-620Crossref Scopus (21) Google Scholar). At these same concentrations, the effect observed on membrane-bound ATPase (F0F1 complex) is restricted to a partial release of inhibition, but the reactivated F0F1complex recovers the ability to couple proton transport to ATP synthesis (24Sigalat C. Pitard B. Haraux F. FEBS Lett. 1995; 368: 253-256Crossref PubMed Scopus (15) Google Scholar). TTX dramatically disturbs the interactions among different nucleotide sites of ATPase, whatever the toxin concentration range (25Fromme P. Dahse I. Gräber P. Z. Naturforsch. 1992; 47c: 239-244Google Scholar, 26Hu N. Mills D.A. Huchzermeyer B. Richter M.L. J. Biol. Chem. 1993; 268: 8536-8540Abstract Full Text PDF PubMed Google Scholar). Simultaneous perturbation of these interactions and preservation of proton coupling in the TTX-reactivated form are intriguing in the context of rotational catalysis. Understanding the inhibitory and reactivating properties of TTX is therefore one of the elements that may contribute to the elucidation of the mechanism of energy coupling. It has been demonstrated (27Pinet E. Gomis J.-M. Girault G. Cavelier F. Verducci J. Noël J.-P. André F. FEBS Lett. 1996; 395: 217-220Crossref PubMed Scopus (17) Google Scholar) that CF1 binds two molecules of TTX on two sites of different affinities, which could be related to the inhibitory and reactivating effects of this molecule. These binding sites have not yet been identified, and the reasons for the specificity of TTX for the CF1-ATP synthase of some higher plants remain obscure (23Dahse I. Pezennec S. Girault D. Berger G. André F. Liebermann B. J. Plant Physiol. 1994; 143: 615-620Crossref Scopus (21) Google Scholar, 28Avni A. Anderson J.D. Holland N. Rochaix J.-D. Gromet-Elhanan Z. Edelman M. Science. 1992; 257: 1245-1247Crossref PubMed Scopus (59) Google Scholar). TTX stabilizes and enhances the ATPase activity of an α3β3 complex from spinach CF1 (29Sokolov M. Gromet-Elhanan Z. Biochemistry. 1996; 35: 1242-1248Crossref PubMed Scopus (23) Google Scholar), which proves that the γ, δ, ε subunits are not required for the stimulation effect of TTX but suggests that they could be necessary for the inhibition. We have shown recently (30Pinet E. Cavelier F. Verducci J. Girault G. Dubart L. Haraux F. Sigalat C. André F. Biochemistry. 1996; 35: 12804-12811Crossref PubMed Scopus (20) Google Scholar) that a very limited change in the molecule of TTX (replacement of l-MeAla1 byl-MeSer1) resulted in a dramatic loss of the reactivating effect at high concentrations, although the inhibitory effect at lower concentrations was unaffected. This led to the idea that it was possible to discriminate inhibitory and activating effects by an appropriate set of molecules derived from TTX. Because high concentrations of MeSer1-TTX were able to prevent CF1-ATPase reactivation by high concentrations of TTX, we proposed that MeSer1-TTX could bind the reactivating site competitively with TTX, giving rise to a poorly active form of the enzyme. However, it cannot be excluded that MeSer1-TTX prevents reactivation simply by chasing TTX from the high affinity site. The question was whether the stimulation by TTX only involves the low affinity binding site or the two binding sites of CF1. To get information about possible cooperation among TTX binding sites, we have used a kinetic approach consisting of studying the catalytic properties of ternary complexes formed by CF1-ε and different TTX analogues. This approach involves various combinations of analogues of different affinities for the inhibitory site and able or not to reactivate the enzyme at high concentrations. The results suggested that both binding sites participate in the formation of the reactivated state. At the same time, we were able to characterize the binding and effector properties of the set of TTX analogues modified in various positions. This allowed us to make hypotheses about the domains of the TTX molecule which are important for binding, inhibition, and stimulation. We thank Véronique Mary for extraction of the spinach chloroplast F1-ATPase. We are indebted to Drs. Florine Cavelier and Jean Verducci for the chemical synthesis of tentoxin and all of its analogues. Dr. Catherine Berthomieu performed the FTIR analysis of tentoxin solutions." @default.
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W1968155346 title "Interrelation between High and Low Affinity Tentoxin Binding Sites in Chloroplast F1-ATPase Revealed by Synthetic Analogues" @default.
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