Boosting cadmium tolerance in Phoebe zhennan: the synergistic effects of exogenous nitrogen and phosphorus treatments promoting antioxidant defense and root development

Plants possess intricate defense mechanisms to resist cadmium (Cd) stress, including strategies like metal exclusion, chelation, osmoprotection, and the regulation of photosynthesis, with antioxidants playing a pivotal role. The application of nitrogen (N) and phosphorus (P) fertilizers are reported to bolster these defenses against Cd stress. Several studies investigated the effects of N or P on Cd stress in non-woody plants and crops. However, the relationship between N, P application, and Cd stress resistance in valuable timber trees remains largely unexplored. This study delves into the Cd tolerance mechanisms of Phoebe zhennan, a forest tree species, under various treatments: Cd exposure alone, combined Cd stress with either N or P and Cd stress with both N and P application. Our results revealed that the P application enhanced root biomass and facilitated the translocation of essential nutrients like K, Mn, and Zn. Conversely, N application, especially under Cd stress, significantly inhibited plant growth, with marked reductions in leaf and stem biomass. Additionally, while the application of P resulted in reduced antioxidant enzyme levels, the combined application of N and P markedly amplified the activities of peroxidase by 266.36%, superoxide dismutase by 168.44%, and ascorbate peroxidase by 26.58% under Cd stress. This indicates an amplified capacity of the plant to neutralize reactive oxygen species. The combined treatment also led to effective regulation of nutrient and Cd distribution in roots, shoots, and leaves, illustrating a synergistic effect in mitigating toxic impact of N. The study also highlights a significant alteration in photosynthetic activities under different treatments. The N addition generally reduced chlorophyll content by over 50%, while P and NP treatments enhanced transpiration rates by up to 58.02%. Our findings suggest P and NP fertilization can manage Cd toxicity by facilitating antioxidant production, osmoprotectant, and root development, thus enhancing Cd tolerance processes, and providing novel strategies for managing Cd contamination in the environment.

Myocardial Glutathione Synthase and TRXIP Expression Are Significantly Elevated in Hypertension and Diabetes: Influence of Stress on Antioxidant Pathways

Antioxidant protection is one of the key reactions of cardiomyocytes (CMCs) in response to myocardial damage of various origins. The thioredoxin interacting protein (TXNIP) is an inhibitor of thioredoxin (TXN). Over the recent few years, TXNIP has received significant attention due to its wide range of functions in energy metabolism. In the present work, we studied the features of the redox-thiol systems, in particular, the amount of TXNIP and glutathione synthetase (GS) as markers of oxidative damage to CMCs and antioxidant protection, respectively. This study was carried out on 38-week-old Wistar-Kyoto rats with insulin-dependent diabetes mellitus (DM) induced by streptozotocin, on 38- and 57-week-old hypertensive SHR rats and on a model of combined hypertension and DM (38-week-old SHR rats with DM). It was found that the amount of TXNIP increased in 57-week-old SHR rats, in diabetic rats and in SHR rats with DM. In 38-week-old SHR rats, the expression of TXNIP significantly decreased. The expression of GS was significantly higher compared with the controls in 57-week-old SHR rats, in DM rats and in the case of the combination of hypertension and DM. The obtained data show that myocardial damage caused by DM and hypertension are accompanied by the activation of oxidative stress and antioxidant protection.

The Regulation of Pea (Pisum sativum L.) Symbiotic Nodule Infection and Defense Responses by Glutathione, Homoglutathione, and Their Ratio

In this study, the roles of glutathione (GSH), homoglutathione (hGSH), and their ratio in symbiotic nodule development and functioning, as well as in defense responses accompanying ineffective nodulation in pea (Pisum sativum) were investigated. The expression of genes involved in (h)GSH biosynthesis, thiol content, and localization of the reduced form of GSH were analyzed in nodules of wild-type pea plants and mutants sym33-3 (weak allele, "locked" infection threads, occasional bacterial release, and defense reactions) and sym33-2 (strong allele, "locked" infection threads, defense reactions), and sym40-1 (abnormal bacteroids, oxidative stress, early senescence, and defense reactions). The effects of (h)GSH depletion and GSH treatment on nodule number and development were also examined. The GSH:hGSH ratio was found to be higher in nodules than in uninoculated roots in all genotypes analyzed, with the highest value being detected in wild-type nodules. Moreover, it was demonstrated, that a hGSHS-to-GSHS switch in gene expression in nodule tissue occurs only after bacterial release and leads to an increase in the GSH:hGSH ratio. Ineffective nodules showed variable GSH:hGSH ratios that correlated with the stage of nodule development. Changes in the levels of both thiols led to the activation of defense responses in nodules. The application of a (h)GSH biosynthesis inhibitor disrupted the nitrogen fixation zone in wild-type nodules, affected symbiosome formation in sym40-1 mutant nodules, and meristem functioning and infection thread growth in sym33-3 mutant nodules. An increase in the levels of both thiols following GSH treatment promoted both infection and extension of defense responses in sym33-3 nodules, whereas a similar increase in sym40-1 nodules led to the formation of infected cells resembling wild-type nitrogen-fixing cells and the disappearance of an early senescence zone in the base of the nodule. Meanwhile, an increase in hGSH levels in sym40-1 nodules resulting from GSH treatment manifested as a restriction of infection similar to that seen in untreated sym33-3 nodules. These findings indicated that a certain level of thiols is required for proper symbiotic nitrogen fixation and that changes in thiol content or the GSH:hGSH ratio are associated with different abnormalities and defense responses.

Gas Chromatography Mass Spectrometry Aided Diagnosis of Glutathione Synthetase Deficiency

Glutathione synthetase (GSS) deficiency is a rare disorder, occurring with a frequency of less than 1 in 100,000 individuals worldwide. The clinical presentation may vary from mild to severe, and manifestations include hemolytic anemia, hyperbilirubinemia, metabolic acidosis, neurological problems, and sepsis. Herein, we present a case of a newborn boy with the most severe phenotype of GSS deficiency, diagnosed based on clinical features and increased urinary 5-oxoproline levels determined via gas chromatography mass spectrometry (GCMS) testing.

Assay of the Enzymes of Glutathione Biosynthesis

This article is dedicated to the late long-time Editor-in-Chief of Analytical Biochemistry, William Jakoby. As a graduate student, I remember reading many articles in Analytical Biochemistry and Methods in Enzymology, both volumes that Bill edited. I first met him as a graduate student presenting at the American Society of Biochemistry (and Molecular Biology) meetings. My Ph.D. advisor, Alton Meister, would bring over well-known biochemists and introduce me as Dr. Anderson, leaving me a bit tongue-tied being that I was still actually a humble graduate student! I next met Bill at my first Analytical Biochemistry Executive Editors meeting in San Diego when he was Editor-in-Chief Emeritus; I felt honored to be on the same board with him and serving the journal to which he had brought to prominence. His eyes were piercing and he was so sharp; his knowledge was both broad and deep. Since much of the large body of Bill's research was on glutathione S-transferases, my article focuses on the assay of the enzymes that synthesize glutathione, a substrate for glutathione S-transferases.

Association between maternal omega-3 polyunsaturated fatty acids supplementation and preterm delivery: A proteomic study

Maternal nutrition during pregnancy influences offspring health. Dietary supplementation of pregnant women with (n-3) long-chain polyunsaturated fatty acids (PUFA) was shown to exert beneficial effects on offspring, through yet unknown mechanisms. Here, we conducted a dietary intervention study on a cohort of 10 women diagnosed with threatened preterm labor with a nutritional integration with eicosapentaenoic and docosahexaenoic acids. Microvesicles (MV) isolated form arterial cord blood of the treated cohort offspring and also of a randomized selection of 10 untreated preterm and 12 term newborns, were characterized by dynamic light scattering and analyzed by proteomic and statistical analysis. Glutathione synthetase was the protein bearing the highest discrimination ability between cohorts. ELISA assay showed that glutathione synthetase was more abundant in cord blood from untreated preterm compared to the other conditions. Assay of free SH-groups showed that serum of preterm subjects was oxidized. Data suggest that preterm suffer from oxidative stress, which was lower in the treated cohort. This study confirms that MV are a representative sample of the individual status and the efficacy of dietary intervention with PUFA in human pregnancy in terms of lowered inflammatory status, increased gestational age and weight at birth.

Comparative Transcriptome Analysis of the Molecular Mechanism of the Hairy Roots of Brassica campestris L. in Response to Cadmium Stress

Brassica campestris L., a hyperaccumulator of cadmium (Cd), is considered a candidate plant for efficient phytoremediation. The hairy roots of Brassica campestris L are chosen here as a model plant system to investigate the response mechanism of Brassica campestris L. to Cd stress. High-throughput sequencing technology is used to identify genes related to Cd tolerance. A total of 2394 differentially expressed genes (DEGs) are identified by RNA-Seq analysis, among which 1564 genes are up-regulated, and 830 genes are down-regulated. Data from the gene ontology (GO) analysis indicate that DEGs are mainly involved in metabolic processes. Glutathione metabolism, in which glutathione synthetase and glutathione S-transferase are closely related to Cd stress, is identified in the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. A Western blot shows that glutathione synthetase and glutathione S-transferase are involved in Cd tolerance. These results provide a preliminary understanding of the Cd tolerance mechanism of Brassica campestris L. and are, hence, of particular importance to the future development of an efficient phytoremediation process based on hairy root cultures, genetic modification, and the subsequent regeneration of the whole plant.

Rice plants have three homologs of glutathione synthetase genes, one of which, OsGS2, codes for hydroxymethyl-glutathione synthetase

Glutathione is a ubiquitous thiol tripeptide in land plants, and glutathione-like tripeptides can also be found in some plant species. Rice (Oryza sativa) plants synthesize hydroxymethyl-glutathione, in which the terminal glycine residue of glutathione is replaced by a serine residue; however, the biosynthetic pathway of hydroxymethyl-glutathione has not been identified. We isolated three rice glutathione synthetase homologs, designated OsGS1, OsGS2, and OsGS3, and found that knockdown of OsGS2 via RNA interference markedly decreased hydroxymethyl-glutathione concentration in rice plants. The in vitro enzyme assay, using purified recombinant protein, demonstrated that OsGS2 catalyzed the synthesis of hydroxymethyl-glutathione from γ-glutamylcysteine (γEC) and L-serine in an ATP-dependent manner. OsGS2 could also utilize glycine as a cosubstrate with γEC, but the enzyme-substrate affinity for L-serine was tenfold higher than that for glycine. These results indicate that OsGS2 codes for hydroxymethyl-glutathione synthetase.

3-Bromo-4,5-dihydroxybenzaldehyde Enhances the Level of Reduced Glutathione via the Nrf2-Mediated Pathway in Human Keratinocytes

A natural bromophenol found in seaweeds, 3-bromo-4,5-dihydroxybenzaldehyde (BDB), has been shown to possess antioxidant effects. This study aimed to investigate the mechanism by which BDB protects skin cells subjected to oxidative stress. The effect of BDB on the protein and mRNA levels of glutathione-related enzymes and the cell survival of human keratinocytes (HaCaT cells) was investigated. BDB treatment increased the protein and mRNA levels of glutathione synthesizing enzymes and enhanced the production of reduced glutathione in HaCaT cells. Furthermore, BDB activated NF-E2-related factor 2 (Nrf2) and promoted its localization into the nucleus by phosphorylating its up-stream signaling proteins, extracellular signal–regulated kinase and protein kinase B. Thus, BDB increased the production of reduced glutathione and established cellular protection against oxidative stress via an Nrf2-mediated pathway.

IncX2 and IncX1-X2 Hybrid Plasmids Coexisting in a FosA6-Producing Escherichia coli Strain

IncX plasmids are receiving much attention as vehicles of carbapenem and colistin resistance genes, such as bla_NDM, bla_KPC, and mcr-1 Among them, IncX2 subgroup plasmids remain rare. Here, we characterized IncX2 and IncX1-X2 hybrid plasmids coexisting in a FosA6-producing Escherichia coli strain that were possibly generated as a consequence of recombination events between an R6K-like IncX2 plasmid and a pLN126_33-like IncX1 plasmid. Variable multidrug resistance mosaic regions were observed in these plasmids, indicating their potential to serve as flexible carriers of resistance genes. The diversity of IncX group plasmid backbones and accessory genes and the evolution of hybrid IncX plasmids pose a challenge in detecting and classifying them.

Stathmin reduction and cytoskeleton rearrangement in rat nucleus accumbens in response to clozapine and risperidone treatment - Comparative proteomic study

The complex network of anatomical connections of the nucleus accumbens (NAc) makes it an interface responsible for the selection and integration of cognitive and affective information to modulate appetitive or aversively motivated behaviour. There is evidence for NAc dysfunction in schizophrenia. NAc also seems to be important for antipsychotic drug action, but the biochemical characteristics of drug-induced alterations within NAc remain incompletely characterized. In this study, a comprehensive proteomic analysis was performed to describe the differences in the mechanisms of action of clozapine (CLO) and risperidone (RIS) in the rat NAc. Both antipsychotics influenced the level of microtubule-regulating proteins, i.e., stathmin, and proteins of the collapsin response mediator protein family (CRMPs), and only CLO affected NAD-dependent protein deacetylase sirtuin-2 and septin 6. Both antipsychotics induced changes in levels of other cytoskeleton-related proteins. CLO exclusively up-regulated proteins involved in neuroprotection, such as glutathione synthetase, heat-shock 70-kDa protein 8 and mitochondrial heat-shock protein 75. RIS tuned cell function by changing the pattern of post-translational modifications of some proteins: it down-regulated the phosphorylated forms of stathmin and dopamine and the cyclic AMP-regulated phosphoprotein (DARPP-32) isoform but up-regulated cyclin-dependent kinase 5 (Cdk5). RIS modulated the level and phosphorylation state of synaptic proteins: synapsin-2, synaptotagmin-1 and adaptor-related protein-2 (AP-2) complex.

The Translational Proteome Modulated by 20(S)-Protopanaxadiol in Endothelial Cells

BACKGROUND

20(S)-protopanaxadiol (PPD), a natural compound of dammarane ginsenoside purified from the ginseng plant, exhibits strong anticancer properties. It has also been reported to have strong antioxidant activity and plays a role in cardiovascular protection. However, the downstream signaling mechanism PPD employs is still unclear and requires further elucidation.

METHODS

Endothelial cells (ECs) EAhy 926 were used to investigate the growth promoting effect of PPD. The protein lysates extracted from both mock- and PPD-treated cells were separated by two-dimensional gel electrophoresis (2-DE) to monitor protein changes. After image analysis, proteins with significant change in the expression level were further identified by mass spectrometry. Western blot was applied to further confirm the protein variations in the 2-DE assay.

RESULTS

In the current study, we found that treatment with PPD (10 μg/ml) significantly increased ECs healing. The translational proteome was established according to 16 up-regulated and 8 down-regulated proteins identified in 2-DE. These proteins were reported to function as energy homeostasis and in the prevention of oxidative stress. The elevated expressions of heme oxygenase 1 (HO-1) and glutathione synthetase (GSS) were further confirmed in the western blot analysis.

CONCLUSIONS

According to the information obtained from translational proteome, we delineated that PPD mediated vascular homeostasis through the up-regulation of anti-oxidative proteins. Additional functional investigations are necessary regarding the HO-1 and GSS proteins.

KEY WORDS

Dammarane sapogenins; Endothelial cell; Glutathione synthetase; Heme oxygenase 1; Proteome; 20(S)-protopanaxadiol.

Immunolocalization of glutathione biosynthesis enzymes in Arabidopsis thaliana

In plants, glutathione serves as a versatile redox buffer and cellular protective compound against a range of biotic and abiotic stresses. Glutathione production involves glutamate-cysteine ligase (GCL), the redox-regulated limiting enzyme of the pathway, and glutathione synthetase (GS). Because the sub-cellular and sub-organellar localization of these enzymes will have an impact on metabolism, here we examine the localization of GCL and GS in the leaves of Arabidopsis thaliana. Immuno-electron microscopy of leaf cells indicates localization of GCL primarily to the chloroplast with GS found in both the chloroplast and cytosol. Detailed examination of the localization of both enzymes within chloroplasts was performed using fractionation followed by immunoblot analysis and indicates that GCL and GS are found in the stroma. The localization of these enzymes to the stroma of chloroplasts has implications for the redox-regulation of GCL and plant glutathione biosynthesis.

The thiol compounds glutathione and homoglutathione differentially affect cell development in alfalfa (Medicago sativa L.)

Glutathione (GSH) is an important scavenger of Reactive Oxygen Species (ROS), precursor of metal chelating phytochelatins, xenobiotic defence compound and regulator of cell proliferation. Homoglutathione (hGSH) is a GSH homologue that is present in several taxa in the family of Fabaceae. It is thought that hGSH performs many of the stress-defence roles typically ascribed to GSH, yet little is known about the potential involvement of hGSH in controlling cell proliferation. Here we show that hGSH/GSH ratios vary across organs and cells and that these changes in hGSH/GSH ratio occur during dedifferentiation and/or cell cycle activation events. The use of a GSH/hGSH biosynthesis inhibitor resulted in impaired cytokinesis in isolated protoplasts, showing the critical importance of these thiol-compounds for cell division. However, exposure of isolated protoplasts to exogenous GSH accelerated cytokinesis, while exogenous hGSH was found to inhibit the same process. We conclude that GSH and hGSH have distinct functional roles in cell cycle regulation in Medicago sativa L. GSH is associated with meristemic cells, and promotes cell cycle activation and induction of somatic embryogenesis, while hGSH is associated with differentiated cells and embryo proliferation.

A novel upregulation of glutathione peroxidase 1 by knockout of liver-regenerating protein Reg3β aggravates acetaminophen-induced hepatic protein nitration

Murine regenerating islet-derived 3β (Reg3β) represents a homologue of human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein and enhances mouse susceptibility to acetaminophen (APAP)-induced hepatotoxicity. Our objective was to determine if and how knockout of Reg3β (KO) affects APAP (300 mg/kg, ip)-mediated protein nitration in mouse liver. APAP injection produced greater levels of hepatic protein nitration in the KO than in the wild-type mice. Their elevated protein nitration was alleviated by a prior injection of recombinant mouse Reg3β protein and was associated with an accelerated depletion of the peroxynitrite (ONOO(-)) scavenger glutathione by an upregulated hepatic glutathione peroxidase-1 (GPX1) activity. The enhanced GPX1 production in the KO mice was mediated by an 85% rise (p<0.05) in the activity of selenocysteine lyase (Scly), a key enzyme that mobilizes Se for selenoprotein biosynthesis. Knockout of Reg3β enhanced AP-1 protein and its binding activity to the Scly gene promoter, upregulating its gene transcription. However, knockout of Reg3β did not affect gene expression of other key factors for selenoprotein biosynthesis. In conclusion, our findings unveil a new metabolic role for Reg3β in protein nitration and a new biosynthesis control of GPX1 by a completely "unrelated" regenerating protein, Reg3β, via transcriptional activation of Scly in coping with hepatic protein nitration. Linking selenoproteins to tissue regeneration will have profound implications in understanding the mechanism of Se functions and physiological coordination of tissue regeneration with intracellular redox control.

Glutathione redox dynamics and expression of glutathione-related genes in the developing embryo

Embryonic development involves dramatic changes in cell proliferation and differentiation that must be highly coordinated and tightly regulated. Cellular redox balance is critical for cell fate decisions, but it is susceptible to disruption by endogenous and exogenous sources of oxidative stress. The most abundant endogenous nonprotein antioxidant defense molecule is the tripeptide glutathione (γ-glutamylcysteinylglycine, GSH), but the ontogeny of GSH concentration and redox state during early life stages is poorly understood. Here, we describe the GSH redox dynamics during embryonic and early larval development (0-5 days postfertilization) in the zebrafish (Danio rerio), a model vertebrate embryo. We measured reduced and oxidized glutathione using HPLC and calculated the whole embryo total glutathione (GSHT) concentrations and redox potentials (Eh) over 0-120 h of zebrafish development (including mature oocytes, fertilization, midblastula transition, gastrulation, somitogenesis, pharyngula, prehatch embryos, and hatched eleutheroembryos). GSHT concentration doubled between 12h postfertilization (hpf) and hatching. The GSH Eh increased, becoming more oxidizing during the first 12h, and then oscillated around -190 mV through organogenesis, followed by a rapid change, associated with hatching, to a more negative (more reducing) Eh (-220 mV). After hatching, Eh stabilized and remained steady through 120 hpf. The dynamic changes in GSH redox status and concentration defined discrete windows of development: primary organogenesis, organ differentiation, and larval growth. We identified the set of zebrafish genes involved in the synthesis, utilization, and recycling of GSH, including several novel paralogs, and measured how expression of these genes changes during development. Ontogenic changes in the expression of GSH-related genes support the hypothesis that GSH redox state is tightly regulated early in development. This study provides a foundation for understanding the redox regulation of developmental signaling and investigating the effects of oxidative stress during embryogenesis.

Salicylic acid increases the contents of glutathione and ascorbate and temporally regulates the related gene expression in salt-stressed wheat seedlings

Exogenous salicylic acid (SA) significantly improved abiotic tolerance in higher plants, and ascorbate (ASA) and glutathione (GSH) play important roles in abiotic tolerance. In this study, SA (0.5mM) markedly increased the contents of ASA and GSH in SA-treated plants during salt stress (250mM NaCl). The transcript levels of the genes encoding ASA and GSH cycle enzymes were measured using quantitative real-time PCR. The results indicated that, during salt stress, exogenous SA significantly enhanced the transcripts of glutathione peroxidase (GPX1), phospholipid hydroperoxide glutathione peroxidase (GPX2) and dehydroascorbate reductase (DHAR) genes at 12h, glutathione reductase (GR) at 24h, 48h and 72h, glutathione-S-transferase 1 (GST1), 2 (GST2), monodehydroascorbate reductase (MDHAR) and glutathione synthetase (GS) at the 48h and 72h after salt stress, respectively. The results implied that SA temporally regulated the transcript levels of the genes encoding ASA-GSH cycle enzymes, resulting in the increased contents of GSH and ASA and enhanced salt tolerance.

5-Oxoprolinuria in Heterozygous Patients for 5-Oxoprolinase (OPLAH) Missense Changes

The inherited 5-oxoprolinuria is primarily suggestive of genetic defects in two enzymes belonging to the gamma-glutamyl cycle in the glutathione (GSH) metabolism: the glutathione synthetase (GSS) and the 5-oxoprolinase (OPLAH). The GSS deficiency is the best characterized of the inborn errors of GSH metabolism, whereas the OPLAH deficiency is questioned whether it is a disorder or just a biochemical condition with no adverse clinical effects. Recently, the first human OPLAH mutation (p.H870Pfs) was reported in homozygosis in two siblings who suffered from 5-oxoprolinuria with a benign clinical course. We report two unrelated patients who manifested massive excretion of 5-oxoproline in urine. In both probands, the blood GSH levels were normal and no mutations were found in the GSS gene. The mutational screening of the OPLAH gene, which included the codified sequences, the intronic flanking sequences, the promoter sequence, and a genetic analysis in order to detect large deletions and/or duplications, showed that each patient only harbors one missense mutation in heterozygosis. The in silico analyses revealed that each one of these OPLAH mutations, p.S323R and p.V1089I, could alter the proper function of this homodimeric enzyme. In addition, clinical symptoms manifest in these two probands were not related to GSH cycle defects and, therefore, this study provides further evidence that oxoprolinuria may present as epiphenomenon in several pathological conditions and confound the final diagnosis.

Improving protein crystal quality by the without-oil microbatch method: crystallization and preliminary X-ray diffraction analysis of glutathione synthetase from Pseudoalteromonas haloplanktis

Glutathione synthetases catalyze the ATP-dependent synthesis of glutathione from l-γ-glutamyl- l-cysteine and glycine. Although these enzymes have been sequenced and characterized from a variety of biological sources, their exact catalytic mechanism is not fully understood and nothing is known about their adaptation at extremophilic environments. Glutathione synthetase from the Antarctic eubacterium Pseudoalteromonas haloplanktis (PhGshB) has been expressed, purified and successfully crystallized. An overall improvement of the crystal quality has been obtained by adapting the crystal growth conditions found with vapor diffusion experiments to the without-oil microbatch method. The best crystals of PhGshB diffract to 2.34 Å resolution and belong to space group P2₁2₁2₁, with unit-cell parameters a = 83.28 Å, b = 119.88 Å, c = 159.82 Å. Refinement of the model, obtained using phases derived from the structure of the same enzyme from Escherichia coli by molecular replacement, is in progress. The structural determination will provide the first structural characterization of a psychrophilic glutathione synthetase reported to date.

Diversification in substrate usage by glutathione synthetases from soya bean (Glycine max), wheat (Triticum aestivum) and maize (Zea mays)

Unlike animals which accumulate glutathione (gamma-glutamyl-L-cysteinyl-glycine) alone as their major thiol antioxidant, several crops synthesize alternative forms of glutathione by varying the carboxy residue. The molecular basis of this variation is not well understood, but the substrate specificity of the respective GSs (glutathione synthetases) has been implicated. To investigate their substrate tolerance, five GS-like cDNAs have been cloned from plants that can accumulate alternative forms of glutathione, notably soya bean [hGSH (homoglutathione or gamma-glutamyl-L-cysteinyl-beta-alanine)], wheat (hydroxymethylglutathione or gamma-glutamyl-L-cysteinyl-serine) and maize (gamma-Glu-Cys-Glu). The respective recombinant GSs were then assayed for the incorporation of differing C-termini into gamma-Glu-Cys. The soya bean enzyme primarily incorporated beta-alanine to form hGSH, whereas the GS enzymes from cereals preferentially catalysed the formation of glutathione. However, when assayed with other substrates, several GSs and one wheat enzyme in particular were able to synthesize a diverse range of glutathione variants by incorporating unusual C-terminal moieties including D-serine, non-natural amino acids and alpha-amino alcohols. Our results suggest that plant GSs are capable of producing a diverse range of glutathione homologues depending on the availability of the acyl acceptor.