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. 2009 Aug 14;284(33):22457-22466.
doi: 10.1074/jbc.M109.010868. Epub 2009 Jun 16.

Relative contributions of cystathionine beta-synthase and gamma-cystathionase to H2S biogenesis via alternative trans-sulfuration reactions

Sangita Singh  1 , Dominique Padovani  1 , Rachel A Leslie  1 , Taurai Chiku  1 , Ruma Banerjee  1
Affiliations

VSports手机版 - Relative contributions of cystathionine beta-synthase and gamma-cystathionase to H2S biogenesis via alternative trans-sulfuration reactions

Sangita Singh et al. J Biol Chem. .

Abstract

In mammals, the two enzymes in the trans-sulfuration pathway, cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE), are believed to be chiefly responsible for hydrogen sulfide (H2S) biogenesis. In this study, we report a detailed kinetic analysis of the human and yeast CBS-catalyzed reactions that result in H2S generation. CBS from both organisms shows a marked preference for H2S generation by beta-replacement of cysteine by homocysteine. The alternative H2S-generating reactions, i VSports手机版. e. beta-elimination of cysteine to generate serine or condensation of 2 mol of cysteine to generate lanthionine, are quantitatively less significant. The kinetic data were employed to simulate the turnover numbers of the various CBS-catalyzed reactions at physiologically relevant substrate concentrations. At equimolar concentrations of CBS and CSE, the simulations predict that H2S production by CBS would account for approximately 25-70% of the total H2S generated via the trans-sulfuration pathway depending on the extent of allosteric activation of CBS by S-adenosylmethionine. The relative contribution of CBS to H2S genesis is expected to decrease under hyperhomocysteinemic conditions. CBS is predicted to be virtually the sole source of lanthionine, and CSE, but not CBS, efficiently cleaves lanthionine. The insensitivity of the CBS-catalyzed H2S-generating reactions to the grade of hyperhomocysteinemia is in stark contrast to the responsiveness of CSE and suggests a previously unrecognized role for CSE in intracellular homocysteine management. Finally, our studies reveal that the profligacy of the trans-sulfuration pathway results not only in a multiplicity of H2S-yielding reactions but also yields novel thioether metabolites, thus increasing the complexity of the sulfur metabolome. .

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Figures

FIGURE 1.
FIGURE 1.
Diversity of reactions catalyzed by the trans-sulfuration pathway. The turnover numbers (v/[E]) estimated at physiological substrate concentrations, i.e. 10 μm homocysteine, 100 μm cysteine, 560 μm serine, and 5 μm cystathionine, are shown in parentheses for each reaction. The thick arrows highlight reactions that are sensitive to elevated levels of homocysteine. The fold change represents the fold increase in the turnover number of a given reaction under conditions of severe hyperhomocysteinemia (200 μm homocysteine).
FIGURE 2.
FIGURE 2.
Reactions catalyzed by CBS leading to cystathionine, lanthionine, and H2S generation that were characterized in this study. The dotted arrows in reactions 2 and 5 denote reactions for which our study did not find evidence.
FIGURE 3.
FIGURE 3.
Kinetics of H2S generation by yCBS. A, kinetics of H2S generation from cysteine and the contributions of reactions 2 and 3 catalyzed by yCBS. The kinetic data for H2S generation from cysteine (reactions 2 + 3) are shown by open circles. Each data point represents the mean (±S.D.) of at least three independent experiments. The data were analyzed as described under “Experimental Procedures,” and the kinetic parameters obtained from these plots are shown in Table 1. The contributions of the component reactions (v2 and v3) to the net rate of H2S generation are shown by gray lines. B, kinetics of H2S production (○) observed at 15 mm cysteine and varying concentrations of homocysteine. Each data point represents the mean (±S.D.) of three independent experiments. The relative contributions of the individual reactions (v2, v3, and v4) to net rate of H2S production were simulated using the kinetic parameters reported in Table 1 and as described under “Experimental Procedures.”
FIGURE 4.
FIGURE 4.
Kinetics of H2S generation by hCBS. A, dependence of H2S generation (reactions 2 + 3) on cysteine concentration. The experimental data are shown by open circles, and the lines represent the fits obtained as described under “Experimental Procedures” for the contributing reaction. B, kinetic dependence of serine (reaction 2, ▵) and lanthionine (reaction 3, ○) generation on cysteine concentration. The lines represent fits obtained as described under “Experimental Procedures.” C, kinetics of H2S production (○) observed at 20 mm cysteine and varying concentrations of homocysteine. Each data point represents the mean (±S.D.) of three independent experiments. The relative contributions of the individual reactions (v2, v3, and v4) to the net rate of H2S production were simulated using the kinetic parameters reported in Table 1 and as described under “Experimental Procedures.”
FIGURE 5.
FIGURE 5.
Relative contributions of fully activated hCBS and CSE to H2S generated via the trans-sulfuration pathway determined by simulations. A, relative proportions of fully activated CBS- and CSE-derived H2S at three concentrations of homocysteine and physiological concentrations of serine, cysteine, and cystathionine. B, relative contributions of fully activated CBS and CSE to net H2S production via the trans-sulfuration pathway at three concentrations of homocysteine mimicking normal (10 μm), moderate (40 μm), and severe (200 μm) hyperhomocysteinemia.
FIGURE 6.
FIGURE 6.
Schematic representation for the sensitivity of the CSE- but not CBS-catalyzed H2S production to hyperhomocysteinemia. Unlike CSE, the PLP-binding pocket of CBS binds serine or cysteine but not homocysteine.
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References

    1. Yang G., Wu L., Jiang B., Yang W., Qi J., Cao K., Meng Q., Mustafa A. K., Mu W., Zhang S., Snyder S. H., Wang R. (2008) Science 322, 587–590 - "VSports" PMC - PubMed
    1. Elrod J. W., Calvert J. W., Morrison J., Doeller J. E., Kraus D. W., Tao L., Jiao X., Scalia R., Kiss L., Szabo C., Kimura H., Chow C. W., Lefer D. J. (2007) Proc. Natl. Acad. Sci. U.S.A. 104, 15560–15565 - PMC - PubMed
    1. Blackstone E., Morrison M., Roth M. B. (2005) Science 308, 518. - "V体育官网入口" PubMed
    1. Sohn H., Kuriyama H. (2001) Yeast 18, 125–135 - "VSports在线直播" PubMed
    1. Mitchell T. W., Savage J. C., Gould D. H. (1993) J. Appl. Toxicol. 13, 389–394 - "V体育2025版" PubMed

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