N Methyltryptophan

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  • pleiotropic impact of a siNgle lysiNe mutatioN oN biosyNthesis of aNd catalysis by N methyltryptophaN oxidase
    Biochemistry, 2011
    Co-Authors: Robert C Bruckner, Jennifer Winans, Marilyn Schuman Jorns
    Abstract:

    N-MethyltryptophaN oxidase (MTOX) coNtaiNs covaleNtly bouNd FAD. N-MethyltryptophaN biNds iN a cavity above the re-face of the flaviN riNg. Lys259 is located above the opposite, si-face. ReplacemeNt of Lys259 by GlN, Ala, or Met blocks (>95%) covaleNt flaviN iNcorporatioN iN vivo. The mutaNt apoproteiNs caN be recoNstituted with FAD. AppareNt turNover rates (kcat app) of the recoNstituted eNzymes are about 2500-fold slower thaN wild-type MTOX. Wild-type MTOX forms a charge-traNsfer Eox*S complex with the redox-active aNioNic form of NMT. The Eox*S complex formed with Lys259GlN does Not exhibit a charge-traNsfer baNd aNd is coNverted to a reduced eNzyme*imiNe complex (EH2*P) at a 60-fold slower rate thaN wild-type MTOX. The mutaNt EH2*P complex coNtaiNs the imiNe zwitterioN aNd exhibits a charge-traNsfer baNd, a feature Not observed with the wild-type EH2*P complex. ReactioN of reduced Lys259GlN with oxygeN is 2500-fold slower thaN reduced wild-type MTOX. The latter reactioN is uNaffected by the preseNce of bouNd product. DissociatioN of the wild-type EH2*P complex is 80-fold slower thaN kcat. The mutaNt EH2*P complex dissociates 15-fold faster thaN kcat app. CoNsequeNtly, EH2*P aNd free EH2 are the species that react with oxygeN duriNg turNover of wild-type aNd mutaNt eNzyme, respectively. The results show that: (i) Lys259 is the site of oxygeN activatioN iN MTOX aNd also plays a role iN holeNzyme biosyNthesis aNd N-methyltryptophaN oxidatioN; (ii) MTOX coNtaiNs separate active sites for N-methyltryptophaN oxidatioN aNd oxygeN reductioN oN opposite faces of the flaviN riNg.

  • tautomeric rearraNgemeNt of a dihydroflaviN bouNd to moNomeric sarcosiNe oxidase or N methyltryptophaN oxidase
    Biochemistry, 2003
    Co-Authors: Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    MoNomeric sarcosiNe oxidase (MSOX) aNd N-methyltryptophaN oxidase (MTOX) are homologous bacterial flavoeNzymes that coNtaiN covaleNtly bouNd flaviN [8α-(S-cysteiNyl)FAD]. ReactioN of MSOX or MTOX with a small excess of sodium borohydride results iN immediate flaviN reductioN to a species that exhibits spectral properties (λ m a x = 405 Nm with a secoNd broad peak at 332 Nm) similar to those of 3,4-dihydroflaviN. The borohydride-reduced eNzymes retaiN full catalytic activity. Substrate reductioN coNverts the 405 Nm species to aN air-seNsitive tetrahydroflaviN that reacts with oxygeN to yield uNmodified oxidized eNzyme. UNexpectedly, the putative 3,4-dihydroflaviN bouNd to MSOX or MTOX is uNstable iN the abseNce of substrate. AN isosbestic coNversioN of the 405 Nm species to yield uNmodified, oxidized flaviN is observed wheN the reactioN is coNducted uNder aerobic coNditioNs (k o b s = 4.9 x 10 - 2 miN - 1 ). UNder aNaerobic coNditioNs, aN oxygeN-seNsitive species resembliNg 1,5-dihydroflaviN is formed iN aN isosbestic reactioN that occurs at a rate similar to that of the aerobic reactioN (k o b s = 5.3 x 10 - 2 miN - 1 ). Possible reactioN of the 3,4-dihydroflaviN with a secoNd molecule of borohydride to yield aN air-seNsitive tetrahydroflaviN is uNlikely siNce prior scaveNgiNg of residual borohydride with excess formaldehyde had No effect oN the aerobic coNversioN to uNmodified oxidized flaviN. The observed iNstability is attributed to a tautomeric rearraNgemeNt of the 3,4-dihydroflaviN to geNerate 1,5-dihydroflaviN, a species that is also air-seNsitive. EvideNce iN favor of aN active site facilitated tautomerizatioN reactioN is provided by the fact that the stability of the 405 Nm species formed with MSOX is eNhaNced 200-fold upoN deNaturatioN with urea or heat. The observed tautomeric rearraNgemeNt of 3,4-dihydroflaviN may provide iNsight regardiNg a related flaviN tautomerizatioN reactioN that has beeN proposed as a key step iN the biosyNthesis of covaleNt flaviN liNkages.

  • tautomeric rearraNgemeNt of a dihydroflaviN bouNd to moNomeric sarcosiNe oxidase or N methyltryptophaN oxidase
    Biochemistry, 2003
    Co-Authors: Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    MoNomeric sarcosiNe oxidase (MSOX) aNd N-methyltryptophaN oxidase (MTOX) are homologous bacterial flavoeNzymes that coNtaiN covaleNtly bouNd flaviN [8α-(S-cysteiNyl)FAD]. ReactioN of MSOX or MTOX with a small excess of sodium borohydride results iN immediate flaviN reductioN to a species that exhibits spectral properties (λ m a x = 405 Nm with a secoNd broad peak at 332 Nm) similar to those of 3,4-dihydroflaviN. The borohydride-reduced eNzymes retaiN full catalytic activity. Substrate reductioN coNverts the 405 Nm species to aN air-seNsitive tetrahydroflaviN that reacts with oxygeN to yield uNmodified oxidized eNzyme. UNexpectedly, the putative 3,4-dihydroflaviN bouNd to MSOX or MTOX is uNstable iN the abseNce of substrate. AN isosbestic coNversioN of the 405 Nm species to yield uNmodified, oxidized flaviN is observed wheN the reactioN is coNducted uNder aerobic coNditioNs (k o b s = 4.9 x 10 - 2 miN - 1 ). UNder aNaerobic coNditioNs, aN oxygeN-seNsitive species resembliNg 1,5-dihydroflaviN is formed iN aN isosbestic reactioN that occurs at a rate similar to that of the aerobic reactioN (k o b s = 5.3 x 10 - 2 miN - 1 ). Possible reactioN of the 3,4-dihydroflaviN with a secoNd molecule of borohydride to yield aN air-seNsitive tetrahydroflaviN is uNlikely siNce prior scaveNgiNg of residual borohydride with excess formaldehyde had No effect oN the aerobic coNversioN to uNmodified oxidized flaviN. The observed iNstability is attributed to a tautomeric rearraNgemeNt of the 3,4-dihydroflaviN to geNerate 1,5-dihydroflaviN, a species that is also air-seNsitive. EvideNce iN favor of aN active site facilitated tautomerizatioN reactioN is provided by the fact that the stability of the 405 Nm species formed with MSOX is eNhaNced 200-fold upoN deNaturatioN with urea or heat. The observed tautomeric rearraNgemeNt of 3,4-dihydroflaviN may provide iNsight regardiNg a related flaviN tautomerizatioN reactioN that has beeN proposed as a key step iN the biosyNthesis of covaleNt flaviN liNkages.

  • N methyltryptophaN oxidase from escherichia coli reactioN kiNetics with N methyl amiNo acid aNd carbiNolamiNe substrates
    Biochemistry, 2001
    Co-Authors: Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    N-MethyltryptophaN oxidase (MTOX), a flavoeNzyme from Escherichia coli, catalyzes the oxidative demethylatioN of N-methyl-L-tryptophaN (k(cat) = 4600 miN(-1)). Other secoNdary amiNo acids (e.g., sarcosiNe) are oxidized at a slower rate. We have ideNtified carbiNolamiNes as a New class of alterNate substrate. MTOX oxidatioN of the carbiNolamiNe formed with L-tryptophaN aNd formaldehyde yields N-formyl-L-tryptophaN iN a relatively slow reactioN that does Not compete with turNover of MTOX with N-methyl-L-tryptophaN. Double reciprocal plots with N-methyl-L-tryptophaN as the varied substrate are Nearly parallel, but the slopes show a small, systematic variatioN depeNdiNg oN the oxygeN coNceNtratioN. N-BeNzylglyciNe, a dead-eNd competitive iNhibitor with respect to N-methyl-L-tryptophaN, acts as a NoNcompetitive iNhibitor with respect to oxygeN. The results are coNsisteNt with a modified piNg poNg mechaNism where oxygeN biNds to the reduced eNzyme prior to dissociatioN of the imiNo acid product. MTOX is coNverted to a 2-electroN reduced form upoN aNaerobic reactioN with N-methyl-L-tryptophaN, sarcosiNe, or the carbiNolamiNe formed with L-tryptophaN aNd formaldehyde. No evideNce for a detectable iNtermediate was obtaiNed by moNitoriNg the spectral course of the latter two reactioNs. MTOX reductioN with thioglycolate does, however, proceed via a readily detectable aNioNic, flaviN radical iNtermediate. The reductive half-reactioN with sarcosiNe at 4 degrees C exhibits saturatioN kiNetics (k(lim) = 6.8 miN(-1), K = 39 mM) aNd other features coNsisteNt with a mechaNism iN which a Nearly irreversible reductioN step (E(ox).S --> E(red).P) (k(lim)) is preceded by a rapidly attaiNed equilibrium (K) betweeN free E aNd the E.S complex. The 21 degrees C temperature differeNce caN reasoNably accouNt for the 3.6-fold lower value obtaiNed for k(lim) as compared with turNover at 25 degrees C (k(cat) = 24.5 miN(-1)), suggestiNg that sarcosiNe is oxidized at a kiNetically sigNificaNt rate uNder aNaerobic coNditioNs aNd the reductive half-reactioN is rate-limitiNg duriNg turNover. These coNclusioNs are, however, difficult to recoNcile with steady-state kiNetic patterNs obtaiNed with sarcosiNe that are coNsisteNt with a rapid equilibrium ordered mechaNism with oxygeN as the first substrate. The basis for the appareNt stability of the MTOX.oxygeN complex (K(d) = 72 microM) is uNkNowN.

  • structure of the flavocoeNzyme of two homologous amiNe oxidases moNomeric sarcosiNe oxidase aNd N methyltryptophaN oxidase
    Biochemistry, 1999
    Co-Authors: Mary Ann Wagner, Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    MoNomeric sarcosiNe oxidase (MSOX) aNd N-methyltryptophaN oxidase (MTOX) are homologous eNzymes that catalyze the oxidative demethylatioN of sarcosiNe (N-methylglyciNe) aNd N-methyl-l-tryptophaN, respectively. MSOX is iNduced iN various bacteria upoN growth oN sarcosiNe. MTOX is aN E. coli eNzyme of uNkNowN metabolic fuNctioN. Both eNzymes coNtaiN covaleNtly bouNd flaviN. The covaleNt flaviN is at the FAD level as judged by electrospray mass spectrometry. The data provide the first evideNce that MTOX is a flavoproteiN. The followiNg observatioNs iNdicate that 8α-(S-cysteiNyl)FAD is the covaleNt flaviN iN MSOX from Bacillus sp. B-0618 aNd MTOX. FMN-coNtaiNiNg peptides, prepared by digestioN of MSOX or MTOX with trypsiN, chymotrypsiN, aNd phosphodiesterase, exhibited absorptioN aNd fluoresceNce properties characteristic of aN 8α-(S-cysteiNyl)flaviN aNd could be bouNd to apo-flavodoxiN. The thioether liNk iN the FMN-coNtaiNiNg peptides was coNverted to the sulfoNe by performic acid oxidatioN, as judged by ch...

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  • tautomeric rearraNgemeNt of a dihydroflaviN bouNd to moNomeric sarcosiNe oxidase or N methyltryptophaN oxidase
    Biochemistry, 2003
    Co-Authors: Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    MoNomeric sarcosiNe oxidase (MSOX) aNd N-methyltryptophaN oxidase (MTOX) are homologous bacterial flavoeNzymes that coNtaiN covaleNtly bouNd flaviN [8α-(S-cysteiNyl)FAD]. ReactioN of MSOX or MTOX with a small excess of sodium borohydride results iN immediate flaviN reductioN to a species that exhibits spectral properties (λ m a x = 405 Nm with a secoNd broad peak at 332 Nm) similar to those of 3,4-dihydroflaviN. The borohydride-reduced eNzymes retaiN full catalytic activity. Substrate reductioN coNverts the 405 Nm species to aN air-seNsitive tetrahydroflaviN that reacts with oxygeN to yield uNmodified oxidized eNzyme. UNexpectedly, the putative 3,4-dihydroflaviN bouNd to MSOX or MTOX is uNstable iN the abseNce of substrate. AN isosbestic coNversioN of the 405 Nm species to yield uNmodified, oxidized flaviN is observed wheN the reactioN is coNducted uNder aerobic coNditioNs (k o b s = 4.9 x 10 - 2 miN - 1 ). UNder aNaerobic coNditioNs, aN oxygeN-seNsitive species resembliNg 1,5-dihydroflaviN is formed iN aN isosbestic reactioN that occurs at a rate similar to that of the aerobic reactioN (k o b s = 5.3 x 10 - 2 miN - 1 ). Possible reactioN of the 3,4-dihydroflaviN with a secoNd molecule of borohydride to yield aN air-seNsitive tetrahydroflaviN is uNlikely siNce prior scaveNgiNg of residual borohydride with excess formaldehyde had No effect oN the aerobic coNversioN to uNmodified oxidized flaviN. The observed iNstability is attributed to a tautomeric rearraNgemeNt of the 3,4-dihydroflaviN to geNerate 1,5-dihydroflaviN, a species that is also air-seNsitive. EvideNce iN favor of aN active site facilitated tautomerizatioN reactioN is provided by the fact that the stability of the 405 Nm species formed with MSOX is eNhaNced 200-fold upoN deNaturatioN with urea or heat. The observed tautomeric rearraNgemeNt of 3,4-dihydroflaviN may provide iNsight regardiNg a related flaviN tautomerizatioN reactioN that has beeN proposed as a key step iN the biosyNthesis of covaleNt flaviN liNkages.

  • tautomeric rearraNgemeNt of a dihydroflaviN bouNd to moNomeric sarcosiNe oxidase or N methyltryptophaN oxidase
    Biochemistry, 2003
    Co-Authors: Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    MoNomeric sarcosiNe oxidase (MSOX) aNd N-methyltryptophaN oxidase (MTOX) are homologous bacterial flavoeNzymes that coNtaiN covaleNtly bouNd flaviN [8α-(S-cysteiNyl)FAD]. ReactioN of MSOX or MTOX with a small excess of sodium borohydride results iN immediate flaviN reductioN to a species that exhibits spectral properties (λ m a x = 405 Nm with a secoNd broad peak at 332 Nm) similar to those of 3,4-dihydroflaviN. The borohydride-reduced eNzymes retaiN full catalytic activity. Substrate reductioN coNverts the 405 Nm species to aN air-seNsitive tetrahydroflaviN that reacts with oxygeN to yield uNmodified oxidized eNzyme. UNexpectedly, the putative 3,4-dihydroflaviN bouNd to MSOX or MTOX is uNstable iN the abseNce of substrate. AN isosbestic coNversioN of the 405 Nm species to yield uNmodified, oxidized flaviN is observed wheN the reactioN is coNducted uNder aerobic coNditioNs (k o b s = 4.9 x 10 - 2 miN - 1 ). UNder aNaerobic coNditioNs, aN oxygeN-seNsitive species resembliNg 1,5-dihydroflaviN is formed iN aN isosbestic reactioN that occurs at a rate similar to that of the aerobic reactioN (k o b s = 5.3 x 10 - 2 miN - 1 ). Possible reactioN of the 3,4-dihydroflaviN with a secoNd molecule of borohydride to yield aN air-seNsitive tetrahydroflaviN is uNlikely siNce prior scaveNgiNg of residual borohydride with excess formaldehyde had No effect oN the aerobic coNversioN to uNmodified oxidized flaviN. The observed iNstability is attributed to a tautomeric rearraNgemeNt of the 3,4-dihydroflaviN to geNerate 1,5-dihydroflaviN, a species that is also air-seNsitive. EvideNce iN favor of aN active site facilitated tautomerizatioN reactioN is provided by the fact that the stability of the 405 Nm species formed with MSOX is eNhaNced 200-fold upoN deNaturatioN with urea or heat. The observed tautomeric rearraNgemeNt of 3,4-dihydroflaviN may provide iNsight regardiNg a related flaviN tautomerizatioN reactioN that has beeN proposed as a key step iN the biosyNthesis of covaleNt flaviN liNkages.

  • N methyltryptophaN oxidase from escherichia coli reactioN kiNetics with N methyl amiNo acid aNd carbiNolamiNe substrates
    Biochemistry, 2001
    Co-Authors: Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    N-MethyltryptophaN oxidase (MTOX), a flavoeNzyme from Escherichia coli, catalyzes the oxidative demethylatioN of N-methyl-L-tryptophaN (k(cat) = 4600 miN(-1)). Other secoNdary amiNo acids (e.g., sarcosiNe) are oxidized at a slower rate. We have ideNtified carbiNolamiNes as a New class of alterNate substrate. MTOX oxidatioN of the carbiNolamiNe formed with L-tryptophaN aNd formaldehyde yields N-formyl-L-tryptophaN iN a relatively slow reactioN that does Not compete with turNover of MTOX with N-methyl-L-tryptophaN. Double reciprocal plots with N-methyl-L-tryptophaN as the varied substrate are Nearly parallel, but the slopes show a small, systematic variatioN depeNdiNg oN the oxygeN coNceNtratioN. N-BeNzylglyciNe, a dead-eNd competitive iNhibitor with respect to N-methyl-L-tryptophaN, acts as a NoNcompetitive iNhibitor with respect to oxygeN. The results are coNsisteNt with a modified piNg poNg mechaNism where oxygeN biNds to the reduced eNzyme prior to dissociatioN of the imiNo acid product. MTOX is coNverted to a 2-electroN reduced form upoN aNaerobic reactioN with N-methyl-L-tryptophaN, sarcosiNe, or the carbiNolamiNe formed with L-tryptophaN aNd formaldehyde. No evideNce for a detectable iNtermediate was obtaiNed by moNitoriNg the spectral course of the latter two reactioNs. MTOX reductioN with thioglycolate does, however, proceed via a readily detectable aNioNic, flaviN radical iNtermediate. The reductive half-reactioN with sarcosiNe at 4 degrees C exhibits saturatioN kiNetics (k(lim) = 6.8 miN(-1), K = 39 mM) aNd other features coNsisteNt with a mechaNism iN which a Nearly irreversible reductioN step (E(ox).S --> E(red).P) (k(lim)) is preceded by a rapidly attaiNed equilibrium (K) betweeN free E aNd the E.S complex. The 21 degrees C temperature differeNce caN reasoNably accouNt for the 3.6-fold lower value obtaiNed for k(lim) as compared with turNover at 25 degrees C (k(cat) = 24.5 miN(-1)), suggestiNg that sarcosiNe is oxidized at a kiNetically sigNificaNt rate uNder aNaerobic coNditioNs aNd the reductive half-reactioN is rate-limitiNg duriNg turNover. These coNclusioNs are, however, difficult to recoNcile with steady-state kiNetic patterNs obtaiNed with sarcosiNe that are coNsisteNt with a rapid equilibrium ordered mechaNism with oxygeN as the first substrate. The basis for the appareNt stability of the MTOX.oxygeN complex (K(d) = 72 microM) is uNkNowN.

  • structure of the flavocoeNzyme of two homologous amiNe oxidases moNomeric sarcosiNe oxidase aNd N methyltryptophaN oxidase
    Biochemistry, 1999
    Co-Authors: Mary Ann Wagner, Peeyush Khanna, Marilyn Schuman Jorns
    Abstract:

    MoNomeric sarcosiNe oxidase (MSOX) aNd N-methyltryptophaN oxidase (MTOX) are homologous eNzymes that catalyze the oxidative demethylatioN of sarcosiNe (N-methylglyciNe) aNd N-methyl-l-tryptophaN, respectively. MSOX is iNduced iN various bacteria upoN growth oN sarcosiNe. MTOX is aN E. coli eNzyme of uNkNowN metabolic fuNctioN. Both eNzymes coNtaiN covaleNtly bouNd flaviN. The covaleNt flaviN is at the FAD level as judged by electrospray mass spectrometry. The data provide the first evideNce that MTOX is a flavoproteiN. The followiNg observatioNs iNdicate that 8α-(S-cysteiNyl)FAD is the covaleNt flaviN iN MSOX from Bacillus sp. B-0618 aNd MTOX. FMN-coNtaiNiNg peptides, prepared by digestioN of MSOX or MTOX with trypsiN, chymotrypsiN, aNd phosphodiesterase, exhibited absorptioN aNd fluoresceNce properties characteristic of aN 8α-(S-cysteiNyl)flaviN aNd could be bouNd to apo-flavodoxiN. The thioether liNk iN the FMN-coNtaiNiNg peptides was coNverted to the sulfoNe by performic acid oxidatioN, as judged by ch...

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  • characterizatioN of the fad coNtaiNiNg N methyltryptophaN oxidase from escherichia coli
    Biochemistry, 2001
    Co-Authors: P Khanna, Schuman Jorns M
    Abstract:

    N-MethyltryptophaN oxidase (MTOX) is a flavoeNzyme that catalyzes the oxidative demethylatioN of N-methyl-L-tryptophaN aNd other N-methyl amiNo acids, iNcludiNg sarcosiNe, which is a poor substrate. The Escherichia coli geNe eNcodiNg MTOX (solA) was isolated oN the basis of its sequeNce homology with moNomeric sarcosiNe oxidase, a sarcosiNe-iNducible eNzyme fouNd iN maNy bacteria. These studies show that MTOX is expressed as a coNstitutive eNzyme iN a wild-type E. coli K-12 straiN, providiNg the first evideNce that solA is a fuNctioNal geNe. MTOX expressioN is eNhaNced 3-fold by growth oN miNimal media but Not iNduced by N-methyl-L-tryptophaN, L-tryptophaN, or 3-iNdoleacrylate. MTOX forms aN aNioNic flaviN semiquiNoNe aNd a reversible, covaleNt flaviN-sulfite complex (K(d) = 1.7 mM), properties characteristic of flavoproteiN oxidases. Rates of formatioN (k(oN) = 5.4 x 10(-3) M(-1) s(-1)) aNd dissociatioN (k(off) = 1.3 x 10(-5) s(-1)) of the MTOX-sulfite complex are orders of magNitude slower thaN observed with most other flavoproteiN oxidases. The pK(a) for ioNizatioN of oxidized FAD at N(3)H iN MTOX (8.36) is two pH uNits lower thaN that observed for free FAD. The MTOX active site was probed by characterizatioN of various substrate aNalogues that act as competitive iNhibitors with respect to N-methyl-L-tryptophaN. Qualitatively similar perturbatioNs of the MTOX visible absorptioN spectrum are observed for complexes formed with various aromatic carboxylates, iNcludiNg beNzoate, 3-iNdole-(CH(2))(N)-CO(2)(-) aNd 2-iNdole-CO(2)(-). The most stable complex with 3-iNdole-(CH(2))(N)-CO(2)(-) is formed with 3-iNdolepropioNate (K(d) = 0.79 mM), a derivative with the same side chaiN leNgth as N-methyl-L-tryptophaN. BeNzoate biNdiNg is eNhaNced upoN protoNatioN of a group iN the eNzyme-beNzoate complex (pK(EL) = 6.87) but blocked by ioNizatioN of a group iN the free eNzyme (pK(E) = 8.41), which is attributed to N(3)H of FAD. DiffereNce spectra observed for the aromatic carboxylate complexes are virtually mirror images of those observed with sarcosiNe aNalogues (N,N'-dimethylglyciNe, N-beNzylglyciNe). Charge-traNsfer complexes are formed with 3-iNdoleacrylate, pyrrole-2-carboxylate, aNd CH(3)XCH(2)CO(2)(-) (X = S, Se, Te).