Involvement of the cystathionine pathway in the biosynthesis of glutathione by isolated rat hepatocytes

Beatty, Patrick W.; Reed, Donald J.

doi:10.1016/0003-9861(80)90009-0

Cited by 148 publications

(85 citation statements)

References 16 publications

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“…1). PPG is a specific suicidal inhibitor of γ-cystathionase, and it has been used extensively in cell culture and mouse model studies as an efficient and specific tool for modulation of TSP activity (14,15). To determine whether PPG targeted and inhibited the TSP in Drosophila, we measured its effect on the levels of GSH, which we have shown previously to be affected by diet.…”

Section: Resultsmentioning

confidence: 99%

Increased transsulfuration mediates longevity and dietary restriction in Drosophila

Kabil

Banerjee

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

132

154

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The mechanisms through which dietary restriction enhances health and longevity in diverse species are unclear. The transsulfuration pathway (TSP) is a highly conserved mechanism for metabolizing the sulfur-containing amino acids, methionine and cysteine. Here we show that Drosophila cystathionine β-synthase (dCBS), which catalyzes the rate-determining step in the TSP, is a positive regulator of lifespan in Drosophila and that the pathway is required for the effects of diet restriction on animal physiology and lifespan. dCBS activity was up-regulated in flies exposed to reduced nutrient conditions, and ubiquitous or neuron-specific transgenic overexpression of dCBS enhanced longevity in fully fed animals. Inhibition of the TSP abrogated the changes in lifespan, adiposity, and protein content that normally accompany diet restriction. RNAi-mediated knockdown of dCBS also limited lifespan extension by diet. Diet restriction reduced levels of protein translation in Drosophila, and we show that this is largely caused by increased metabolic commitment of methionine cycle intermediates to transsulfuration. However, dietary supplementation of methionine restored normal levels of protein synthesis to restricted animals without affecting lifespan, indicating that global reductions in translation alone are not required for diet-restriction longevity. Our results indicate a mechanism by which dietary restriction influences physiology and aging.hydrogen sulfide | essential amino acids | metabolism | healthspan F or a broad range of taxonomically diverse organisms, the quality of their diet acts as a powerful modulator of health and longevity through molecular mechanisms that are largely unknown. Lifespan is extended, for example, when food is restricted to an extent that falls short of inducing starvation. In mammals, this manipulation, which is often called dietary restriction (DR), not only increases lifespan but also imparts a broad-spectrum improvement in health during aging. In humans, for example, DR reduces risk factors for diabetes, cardiovascular disease, and cancer (1).Transsulfuration is an evolutionarily ancient metabolic process that involves a network of enzymes responsible for the metabolism of sulfur-containing amino acids. The transsulfuration pathway (TSP) has been studied extensively in mammals, in which it has been shown to direct the conversion of homocysteine to cysteine following the breakdown of methionine, an essential amino acid. Flux through the TSP is known to affect overall cellular metabolism by directly influencing cysteine and methionine levels. Methionine availability affects protein synthesis and methylation, and it has been implicated in murine aging (2). Cysteine availability controls the synthesis of glutathione (GSH), which is the chief regulator of cellular redox homeostasis and an important agent in xenobiotic detoxification (Fig. 1A). Patients with genetic defects in the TSP are characterized by high levels of homocysteine, low levels of GSH, and increased incidence of age-related path...

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Section: Resultsmentioning

confidence: 99%

Increased transsulfuration mediates longevity and dietary restriction in Drosophila

Kabil

Banerjee

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

132

154

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“…In the absence of cysteine, however, no increase in the neuronal GSH concentration was observed when glutamine was supplied (42). Methionine is an important amino acid for producing cysteine via the trans-sulfuration pathway, which supplies approximately 50% of the cysteine needed for GSH synthesis in the liver (45). However, the brain trans-sulfuration pathway is thought to be negligible because the pathway-related enzymatic activity and RNA expression were found to be much lower than those in the liver (46).…”

Section: Gsh Synthesismentioning

confidence: 99%

Regulation of Neuronal Glutathione Synthesis

2008

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Abstract. The brain is among the major organs generating large amounts of reactive oxygen species and is especially susceptible to oxidative stress. Glutathione (GSH) plays critical roles as an antioxidant, enzyme cofactor, cysteine storage form, the major redox buffer, and a neuromodulator in the central nervous system. GSH deficiency has been implicated in neurodegenerative diseases. GSH is a tripeptide comprised of glutamate, cysteine, and glycine. Cysteine is the rate-limiting substrate for GSH synthesis within neurons. Most neuronal cysteine uptake is mediated by sodium-dependent excitatory amino acid transporter (EAAT) systems, known as excitatory amino acid carrier 1 (EAAC1). Previous studies demonstrated EAAT is vulnerable to oxidative stress, leading to impaired function. A recent study found EAAC1-deficient mice to have decreased brain GSH levels and increased susceptibility to oxidative stress. The function of EAAC1 is also regulated by glutamate transporter associated protein 3-18. This review focuses on the mechanisms underlying GSH synthesis, especially those related to neuronal cysteine transport via EAAC1, as well as on the importance of GSH functions against oxidative stress.

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“…Under conditions of plenty, methionine is directed toward cysteine synthesis via the transsulfuration pathway for use in glutathione and other cellular functions or directed toward catabolism. Cysteine is the limiting reagent in glutathione synthesis and in liver; Ϸ50% of the cysteine in glutathione is derived from methionine via the transsulfuration pathway (6)(7)(8). Conversely, it is expected that when methionine levels are low, flux through the transsulfuration pathway is down-regulated to conserve the amino acid backbone in the methionine cycle (9).…”

mentioning

confidence: 99%

S -adenosylmethionine stabilizes cystathionine β-synthase and modulates redox capacity

Prudova

Bauman

Braun

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

220

202

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The transsulfuration pathway converts homocysteine to cysteine and represents the metabolic link between antioxidant and methylation metabolism. The first and committing step in this pathway is catalyzed by cystathionine ␤-synthase (CBS), which is subject to complex regulation, including allosteric activation by the methyl donor, S-adenosylmethionine (AdoMet). In this study, we demonstrate that methionine restriction leads to a >10-fold decrease in CBS protein levels, and pulse proteolysis studies reveal that binding of AdoMet stabilizes the protein against degradation by Ϸ12 kcal͞mol. These observations predict that under pathological conditions where AdoMet levels are diminished, CBS, and therefore glutathione levels, will be reduced. Indeed, we demonstrate this to be the case in a mouse model for spontaneous steatohepatitis in which the gene for the MAT1A isoenzyme encoding AdoMet synthetase has been disrupted, and in human hepatocellular carcinoma, where MAT1A is silenced. Furthermore, diminished CBS levels are associated with reduced cell viability in hepatoma cells challenged with tert-butyl hydroperoxide. This study uncovers a mechanism by which CBS is allosterically activated by AdoMet under normal conditions but is destabilized under pathological conditions, for redirecting the metabolic flux toward methionine conservation. A mechanistic basis for the coordinate changes in redox and methylation metabolism that are a hallmark of several complex diseases is explained by these observations. glutathione ͉ liver disease C ellular methylation and antioxidant metabolism are linked by the transsulfuration pathway, which converts the methionine cycle intermediate, homocysteine, to cysteine, the limiting reagent in glutathione synthesis. The balance between conserving methionine via transmethylation under conditions of methionine restriction and committing it to transsulfuration under conditions of plenty is regulated at two key control points, methionine adenosyltransferase (MAT) and cystathionine ␤-synthase (CBS) (Fig. 1). Aberrations in methylation and redox homeostasis are common to a number of chronic diseases including pathologies of the liver. In alcoholic liver disease and in hepatocellular carcinoma an increase in markers of oxidative stress is observed (1, 2). Furthermore, there is a switch in the expression of MAT genes from MAT1A to MAT2A in liver cancer, which correlates with lower S-adenosylmethionine (AdoMet) levels (3).Under normal conditions, coordinate regulation of methylation and antioxidant metabolism is achieved by the allosteric activation of CBS by AdoMet (Fig. 1). AdoMet is a V-type allosteric effector that increases CBS activity 2-to 3-fold (4, 5). Under conditions of plenty, methionine is directed toward cysteine synthesis via the transsulfuration pathway for use in glutathione and other cellular functions or directed toward catabolism. Cysteine is the limiting reagent in glutathione synthesis and in liver; Ϸ50% of the cysteine in glutathione is derived from methionine via the transsulf...

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Involvement of the cystathionine pathway in the biosynthesis of glutathione by isolated rat hepatocytes

Cited by 148 publications

References 16 publications

Increased transsulfuration mediates longevity and dietary restriction in Drosophila

Increased transsulfuration mediates longevity and dietary restriction in Drosophila

Regulation of Neuronal Glutathione Synthesis

S -adenosylmethionine stabilizes cystathionine β-synthase and modulates redox capacity

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