[35S]GTPγS (Guanosine-5'-O-(γ-thio)triphosphate-[35S]) Binding Scintillation Proximity Assay Experiments in Postmortem Brain Tissue.

Heterotrimeric guanine nucleotide-binding proteins (G proteins) are the very first effector in signal transduction events triggered by G-protein-coupled receptors (GPCRs). One of the most widely used approaches for determining GPCR activity in native tissue is based on the binding of [35S]GTPγS. Classically, an heterogeneous procedure including a filtration step has been used, but a modification of the protocol including an immunoprecipitation step has allowed the specific discrimination of the contribution of the different Gα subunit subtypes to the effect of each ligand. Nowadays, that the concept of functional selectivity has been demonstrated for several ligands and GPCRs, information obtained from this methodological approach will be very useful for broadening the knowledge of GPCRs signaling profiles and describing the effect of different ligands over them. In this chapter we will describe the detailed protocol of antibody-capture [35S]GTPγS scintillation proximity assay (SPA) in order to provide the reader with comprehensive guidelines to study receptor-mediated functional activation of different Gα-protein subtypes in native mammalian brain membranes. In addition, advantages and limitations of this method will be described, as well as future direction in the application of this approach indicated.

Assay of GTPγS Binding in Autoradiography.

Autoradiography of radiolabeled GTPγS ([35S]GTPγS) binding is a relevant technique to study the function of G protein-coupled receptors (GPCRs) ex vivo. Here, we describe the protocol for such a method, suitable for investigating CB1 receptor functionality in tissue slices from rodent brains.

Rapid metabolism fosters microbial survival in the deep, hot subseafloor biosphere.

A fourth of the global seabed sediment volume is buried at depths where temperatures exceed 80 °C, a previously proposed thermal barrier for life in the subsurface. Here, we demonstrate, utilizing an extensive suite of radiotracer experiments, the prevalence of active methanogenic and sulfate-reducing populations in deeply buried marine sediment from the Nankai Trough subduction zone, heated to extreme temperature (up to ~120 °C). The small microbial community subsisted with high potential cell-specific rates of energy metabolism, which approach the rates of active surface sediments and laboratory cultures. Our discovery is in stark contrast to the extremely low metabolic rates otherwise observed in the deep subseafloor. As cells appear to invest most of their energy to repair thermal cell damage in the hot sediment, they are forced to balance delicately between subsistence near the upper temperature limit for life and a rich supply of substrates and energy from thermally driven reactions of the sedimentary organic matter.

GTPγS-Autoradiography for Studies of Opioid Receptor Functionality.

The opioid receptors have been an interesting target for the drug industry for decades. These receptors were pharmacologically characterized in the 1970s and several drugs and peptides have emerged over the years. In 2012, the crystal structures were also demonstrated, with new data on the receptor sites, and thus new possibilities will appear. The role of opioids in the brain has attracted considerable interest in several diseases, especially pain and drug dependence. The opioid receptors are G-protein-coupled receptors (GPCR ) that are Gi coupled which make them suitable for studying the receptor functionality. The [35S]GTP γS autoradiography assay is a good option that has the benefit of generating both anatomical and functional data in the area of interest. It is based on the first step of the signaling mechanism of GPCRs. When a ligand binds to the receptor GTP will replace GDP on the a-subunit of the G-protein, leading to a dissociation of the ßγ-subunit. These subunits will start a cascade of second messengers and subsequently a physiological response.

Acute Exposure to SiO2 Nanoparticles Affects Protein Synthesis in Bergmann Glia Cells.

Attractive due to an alleged high biocompatibility, silica nanoparticles have been widely used in the field of nanomedicine; however, their proven capacity to induce the synthesis and release of pro-inflammatory cytokines in several cellular models has raised concern about their safety. Glutamate, the main excitatory amino acid transmitter triggers a wide variety of signal transduction cascades that regulate protein synthesis at transcriptional and translational levels. A stimulus-dependent dynamic change in the protein repertoire in neurons and glia cells is the molecular framework of higher brain functions. Within the cerebellum, Bergmann glia cells are the most abundant non-neuronal cells and span the entire molecular layer of the cerebellar cortex, wrapping the synapses in this structure. Taking into consideration the functional role of Bergmann glia in terms of the recycling of glutamate, lactate supply to neurons, and prevention of neurotoxic insults, we decided to investigate the possibility that silica nanoparticles affect Bergmann glia and by these means alter the major excitatory neurotransmitter system in the brain. To this end, we exposed cultured chick cerebellar Bergmann glia cells to silica nanoparticles and measured [35S]-methionine incorporation into newly synthesized polypeptides. Our results demonstrate that exposure of the cultured cells to silica nanoparticles exerts a time- and dose-dependent modulation of protein synthesis. Furthermore, altered patterns of eukaryotic initiation factor 2 alpha and eukaryotic elongation factor 2 phosphorylation were present upon nanoparticle exposure. These results demonstrate that glia cells respond to the presence of this nanomaterial modifying their proteome, presumably in an effort to overcome any plausible neurotoxic effect.

Big Data Challenges Targeting Proteins in GPCR Signaling Pathways; Combining PTML-ChEMBL Models and [35S]GTPγS Binding Assays.

G-protein-coupled receptors (GPCRs), also known as 7-transmembrane receptors, are the single largest class of drug targets. Consequently, a large amount of preclinical assays having GPCRs as molecular targets has been released to public sources like the Chemical European Molecular Biology Laboratory (ChEMBL) database. These data are also very complex covering changes in drug chemical structure and assay conditions like c0 = activity parameter (Ki, IC50, etc.), c1 = target protein, c2 = cell line, c3 = assay organism, etc., making difficult the analysis of these databases that are placed in the borders of a Big Data challenge. One of the aims of this work is to develop a computational model able to predict new GPCRs targeting drugs taking into consideration multiple conditions of assay. Another objective is to perform new predictive and experimental studies of selective 5-HTA2 receptor agonist, antagonist, or inverse agonist in human comparing the results with those from the literature. In this work, we combined Perturbation Theory (PT) and Machine Learning (ML) to seek a general PTML model for this data set. We analyzed 343 738 unique compounds with 812 072 end points (assay outcomes), with 185 different experimental parameters, 592 protein targets, 51 cell lines, and/or 55 organisms (species). The best PTML linear model found has three input variables only and predicted 56 202/58 653 positive outcomes (sensitivity = 95.8%) and 470 230/550 401 control cases (specificity = 85.4%) in training series. The model also predicted correctly 18 732/19 549 (95.8%) of positive outcomes and 156 739/183 469 (85.4%) of cases in external validation series. To illustrate its practical use, we used the model to predict the outcomes of six different 5-HT2A receptor drugs, namely, TCB-2, DOI, DOB, altanserin, pimavanserin, and nelotanserin, in a very large number of different pharmacological assays. 5-HT2A receptors are altered in schizophrenia and represent drug target for antipsychotic therapeutic activity. The model correctly predicted 93.83% (76 of 86) experimental results for these compounds reported in ChEMBL. Moreover, [35S]GTPγS binding assays were performed experimentally with the same six drugs with the aim of determining their potency and efficacy in the modulation of G-proteins in human brain tissue. The antagonist ketanserin was included as inactive drug with demonstrated affinity for 5-HT2A/C receptors. Our results demonstrate that some of these drugs, previously described as serotonin 5-HT2A receptor agonists, antagonists, or inverse agonists, are not so specific and show different intrinsic activity to that previously reported. Overall, this work opens a new gate for the prediction of GPCRs targeting compounds.

Increased sensitivity to Δ9-THC-induced rewarding effects after seven-week exposure to electronic and tobacco cigarettes in mice.

Cigarette (CIG) smoking often precedes the use of illegal drugs. Electronic-cigarettes (e-CIGs) have been promoted as a means of stopping smoking and reducing the harmful effects of CIGs on the population. However, although e-CIGs eliminate some of the morbidity associated with combustible tobacco, they are still nicotine-delivery devices. In order to study whether the nicotine delivered via e-CIG acts as "a gateway drug" to the use of cannabis, we analysed the behavioural and molecular effects of 7 weeks' pre-exposure to air (AIR), e-CIGs or CIGs on addiction-related conditioned place preference (CPP) in mice using a sub-threshold (0.01 mg/kg) dose of delta-9-tetrahydrocannabinol (Δ9-THC), the principal psychoactive constituent of cannabis. After 8 and 66 days of withdrawal, this Δ9-THC dose was ineffective in inducing CPP in mice pre-exposed to pump-driven AIR, but very effective in mice pre-exposed to e-CIGs or CIGs. Exposure to e-CIGs or CIGs increases the expression of ΔFosB in the nucleus accumbens (NAc), which remains high during short-term e-CIG or CIG withdrawal and long-term CIG withdrawal and is not influenced by treatment with Δ9-THC. At the end of e-CIG or CIG exposure and during withdrawal, the mice also had a higher AMPA receptors GluA1/GluA2-3 ratio in the NAc. Chronic nicotine exposure increases sensitivity to rewarding effects of Δ9-THC in mice and produces long-lasting neurobiological changes regardless of the delivery method (CIG vs. e-CIG). The exposure to passive tobacco smoke or e-CIG vapours can similarly increase vulnerability to the effects of cannabis and possibly other drugs of abuse.

The subcommissural organ and the Reissner fiber: old friends revisited.

The subcommissural organ (SCO) is an ancient and conserved brain gland secreting into cerebrospinal fluid (CSF) glycoproteins that form the Reissner fiber (RF). The present investigation was designed to further investigate the dynamic of the biosynthetic process of RF glycoproteins prior and after their release into the CSF, to identify the RF proteome and N-glycome and to clarify the mechanism of assembly of RF glycoproteins. Various methodological approaches were used: biosynthetic labelling injecting 35S-cysteine and 3H-galactose into the CSF, injection of antibodies against galectin-1 into the cerebrospinal fluid, light and electron microscopical methods; isolated bovine RF was used for proteome analyses by mass spectrometry and glycome analysis by xCGE-LIF. The biosynthetic labelling study further supported that a small pool of SCO-spondin molecules rapidly enter the secretory pathways after its synthesis, while most of the SCO-spondin molecules are stored in the rough endoplasmic reticulum for hours or days before entering the secretory pathway and being released to assemble into RF. The proteomic analysis of RF revealed clusterin and galectin-1 as partners of SCO-spondin; the in vivo use of anti-galectin-1 showed that this lectin is essential for the assembly of RF. Galectin-1 is not secreted by the SCO but evidence was obtained that it would be secreted by multiciliated ependymal cells lying close to the SCO. Further, a surprising variety and complexity of glycan structures were identified in the RF N-glycome that further expands the potential functions of RF to a level not previously envisaged. A model of the macromolecular organization of Reissner fiber is proposed.

Pulse-Chase Labeling of Protein Antigens with [35S]Methionine.

Pulse-chase labeling of antigens with [35S]methionine is used to determine the relative half-life of a protein. In this protocol, intracellular unlabeled methionine levels are reduced by starvation of cells for 0.5-1 h, and then the cells are briefly labeled with [35S]methionine to create the pulse of newly synthesized proteins. Upon completion of cell labeling, the addition of Chasing medium containing an excess of unlabeled methionine is used to create the chase, reducing the likelihood that any remaining [35S]methionine will be incorporated into newly synthesized proteins. Labeling and chasing reactions of adherent cells can be directly performed in cell culture dishes in an incubator, whereas suspension cells are labeled and chased in a polypropylene tube kept in a water bath set at 37°C. At intervals after the pulse, aliquots of chased labeled cells are collected and pelleted with the option of immediately preparing cell lysates or freezing and storing the cell pellets at -80°C. Upon cell lysis and antigen purification by immunoprecipitation, SDS-PAGE-resolved proteins can be fixed on the gel and enhanced with fluorography or can be transferred to a nitrocellulose or polyvinylidene fluoride (PVDF) membrane followed by autoradiography or exposure in a phosphorimager. Membrane blotting has the advantage of allowing for detection of the target of interest by probing with an antigen-specific antibody to confirm that equal amounts of steady-state levels of the target protein were immunoprecipitated at each interval.

Functional coupling between adenosine A1 receptors and G-proteins in rat and postmortem human brain membranes determined with conventional guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding or [35S]GTPγS/immunoprecipitation assay.

Adenosine signaling plays a complex role in multiple physiological processes in the brain, and its dysfunction has been implicated in pathophysiology of neuropsychiatric diseases such as schizophrenia and affective disorders. In the present study, the coupling between adenosine A1 receptor and G-protein was assessed by means of two [35S]GTPγS binding assays, i.e., conventional filtration method and [35S]GTPγS binding/immunoprecipitation in rat and human brain membranes. The latter method provides information about adenosine A1 receptor-mediated Gαi-3 activation in rat as well as human brain membranes. On the other hand, adenosine-stimulated [35S]GTPγS binding determined with conventional assay derives from functional activation of Gαi/o proteins (not restricted only to Gαi-3) coupled to adenosine A1 receptors. The determination of adenosine concentrations in the samples used in the present study indicates the possibility that the assay mixture under our experimental conditions contains residual endogenous adenosine at nanomolar concentrations, which was also suggested by the results on the effects of adenosine receptor antagonists on basal [35S]GTPγS binding level. The effects of adenosine deaminase (ADA) on basal binding also support the presence of adenosine. Nevertheless, the varied patterns of ADA discouraged us from adding ADA into assay medium routinely. The concentration-dependent increases elicited by adenosine were determined in 40 subjects without any neuropsychiatric disorders. The increases in %Emax values determined by conventional assay according to aging and postmortem delay should be taken into account in future studies focusing on the effects of psychiatric disorders on adenosine A1 receptor/G-protein interaction in postmortem human brain tissue.

Prenatal Alcohol Exposure Increases Histamine H3 Receptor-Mediated Inhibition of Glutamatergic Neurotransmission in Rat Dentate Gyrus.

BACKGROUND: We have reported that prenatal alcohol exposure (PAE)-induced deficits in dentate gyrus, long-term potentiation (LTP), and memory are ameliorated by the histamine H3 receptor inverse agonist ABT-239. Curiously, ABT-239 did not enhance LTP or memory in control offspring. Here, we initiated an investigation of how PAE alters histaminergic neurotransmission in the dentate gyrus and other brain regions employing combined radiohistochemical and electrophysiological approaches in vitro to examine histamine H3 receptor number and function. METHODS: Long-Evans rat dams voluntarily consumed either a 0% or 5% ethanol solution 4 hours each day throughout gestation. This pattern of drinking, which produces a mean peak maternal serum ethanol concentration of 60.8 ± 5.8 mg/dl, did not affect maternal weight gain, litter size, or offspring birthweight. RESULTS: Radiohistochemical studies in adult offspring revealed that specific [3 H]-A349821 binding to histamine H3 receptors was not different in PAE rats compared to controls. However, H3 receptor-mediated Gi /Go protein-effector coupling, as measured by methimepip-stimulated [35 S]-GTPγS binding, was significantly increased in cerebral cortex, cerebellum, and dentate gyrus of PAE rats compared to control. A LIGAND analysis of detailed methimepip concentration-response curves in dentate gyrus indicated that PAE significantly elevates receptor-effector coupling by a lower affinity H3 receptor population without significantly altering the affinities of H3 receptor subpopulations. In agreement with the [35 S]-GTPγS studies, a similar range of methimepip concentrations also inhibited electrically evoked field excitatory postsynaptic potential responses and increased paired-pulse ratio, a measure of decreased glutamate release, to a significantly greater extent in dentate gyrus slices from PAE rats than in controls. CONCLUSIONS: These results suggest that a PAE-induced elevation in H3 receptor-mediated inhibition of glutamate release from perforant path terminals as 1 mechanism contributing the LTP deficits previously observed in the dentate gyrus of PAE rats, as well as providing a mechanistic basis for the efficacy of H3 receptor inverse agonists for ameliorating these deficits.

Pulse-Chase Biosynthetic Radiolabeling of Pancreatic Islets to Measure Beta Cell Function.

Pulse-chase radiolabeling of cells with radioactive amino acids is a common method for studying the biosynthesis of proteins. The labeled proteins can then be immunoprecipitated and analyzed by electrophoresis and gel imaging techniques. This chapter presents a protocol for the biosynthetic labeling and immunoprecipitation of pancreatic islet proteins which are known to be affected in disorders such as diabetes, obesity, and metabolic syndrome.

ABIN-1 Negatively Regulates µ-Opioid Receptor Function.

The µ-opioid receptor (MOR) is a Gi/o protein-coupled receptor that mediates analgesic, euphoric, and reward effects. Using a bacterial two-hybrid screen, we reported that the carboxyl tail of the rat MOR associates with A20-binding inhibitor of nuclear factor κB (ABIN-1). This interaction was confirmed by direct protein-protein binding and coimmunoprecipitation of MOR and ABIN-1 proteins in cell lysates. Saturation binding studies showed that ABIN-1 had no effect on MOR binding. However, the interaction of ABIN-1 and MOR inhibited the activation of G proteins induced by DAMGO ([d-Ala2,N-Me-Phe4,Gly5-ol]-Enkephalin). MOR phosphorylation, ubiquitination, and internalization induced by DAMGO were decreased in Chinese hamster ovary cells that coexpressed MOR and ABIN-1. The suppression of forskolin-stimulated adenylyl cyclase by DAMGO was also inhibited by the interaction of ABIN-1 with MOR. In addition, extracellular signal-regulated kinase activation was also negatively regulated by overexpression of ABIN-1. These data suggest that ABIN-1 is a negative coregulator of MOR activation, phosphorylation, and internalization in vitro. ABIN-1 also inhibited morphine-induced hyperlocomotion in zebrafish larvae (AB strain). By utilization of an antisense morpholino oligonucleotide (MO) gene knockdown technology, the ABIN-1 MO-injected zebrafish larvae showed a significant increase (approximately 60%) in distance moved compared with control MO-injected larvae after acute morphine treatment (P < 0.01). Taken together, ABIN-1 negatively regulates MOR function in vitro and in vivo.

Metabolic Labeling of Protein Antigens with [35S]Methionine.

Metabolic labeling of antigens can be achieved by supplementation of the cell culture medium with radioactive amino acid precursors such as [35S]methionine during the incubation period of target cells. In this protocol, intracellular unlabeled methionine levels are reduced by starvation of cells for 0.5-1 h before the addition of labeled [35S]methionine and incubation for 0.5-4 h. Upon completion of the metabolic labeling process, cells can be prepared for immunoprecipitation by lysis or alternatively pelleted and frozen for cell lysate preparations at a later time.

In vivo and in vitro evaluation of novel µ-opioid receptor agonist compounds.

Opioids are the most effective and widely used drugs for pain treatment. Morphine is an archetypal opioid and is an opioid receptor agonist. Unfortunately, the clinical usefulness of morphine is limited by adverse effects such as analgesic tolerance and addiction. Therefore, it is important to study the development of novel opioid agonists as part of pain control. The analgesic effects of opioids are mediated by three opioid receptors, namely opioid µ-, δ-, and κ-receptors. They belong to the G protein-coupled receptor superfamily and are coupled to Gi proteins. In the present study, we developed a ligand screening system to identify novel opioid µ-receptor agonists that measures [(35)S]GTPγS binding to cell membrane fractions prepared from the fat body of transgenic silkworms expressing µ-receptor-Gi1α fusion protein. We screened the RIKEN Natural Products Depository (NPDepo) chemical library, which contains 5848 compounds, and analogs of hit compounds. We successfully identified a novel, structurally unique compound, that we named GUM1, with agonist activity for the opioid µ-receptor (EC50 of 1.2 µM). The Plantar Test (Hargreaves' Method) demonstrated that subcutaneous injection of 3mg/kg of GUM1 into wild-type rats significantly extended latency time. This extension was also observed in a rat model of morphine tolerance and was inhibited by pre-treatment of naloxone. The unique molecular skeleton of GUM1 makes it an attractive molecule for further ligand-opioid receptor binding studies.

Altered CB1 receptor coupling to G-proteins in the post-mortem caudate nucleus and cerebellum of alcoholic subjects.

Biochemical, pharmacological and genetic evidence suggests the involvement of the endocannabinoid system in alcohol dependence. The aim of the present study was to evaluate the state of CB1 receptors in post-mortem caudate nucleus, hippocampus and cerebellum of alcoholic subjects.CB1 protein levels were measured by Western blot, CB1 receptor density and affinity by [(3)H]WIN55,212-2 saturation assays and CB1 functionality by [(35)S]GTPγS binding assays. Experiments were performed in samples from 24 subjects classified as non-suicidal alcoholics (n = 6), suicidal alcoholics (n = 6), non-alcoholic suicide victims (n = 6) and control subjects (n = 6).Alcoholic subjects presented hyperfunctional CB1 receptors in the caudate nucleus resulting in a higher maximal effect in both alcoholic groups compared to the non-alcoholic groups (p < 0.001). Conversely, in the cerebellum the non-suicidal alcoholic subjects showed hypofunctional receptors with lower maximal effect and potency (p < 0.001). No changes were found in the CB1 protein expression in either region. In the hippocampus of alcoholic subjects, no changes were observed either in the functionality, density or protein levels.Our data support an association between endocannabinoid system activity and alcoholism. The modifications reported here could be either a consequence of high lifetime ethanol consumption or a vulnerability factor to develop alcohol addiction.

Nitrogen-Fixing Nodules Are an Important Source of Reduced Sulfur, Which Triggers Global Changes in Sulfur Metabolism in Lotus japonicus.

We combined transcriptomic and biochemical approaches to study rhizobial and plant sulfur (S) metabolism in nitrogen (N) fixing nodules (Fix(+)) of Lotus japonicus, as well as the link of S-metabolism to symbiotic nitrogen fixation and the effect of nodules on whole-plant S-partitioning and metabolism. Our data reveal that N-fixing nodules are thiol-rich organs. Their high adenosine 5'-phosphosulfate reductase activity and strong (35)S-flux into cysteine and its metabolites, in combination with the transcriptional upregulation of several rhizobial and plant genes involved in S-assimilation, highlight the function of nodules as an important site of S-assimilation. The higher thiol content observed in nonsymbiotic organs of N-fixing plants in comparison to uninoculated plants could not be attributed to local biosynthesis, indicating that nodules are an important source of reduced S for the plant, which triggers whole-plant reprogramming of S-metabolism. Enhanced thiol biosynthesis in nodules and their impact on the whole-plant S-economy are dampened in plants nodulated by Fix(-) mutant rhizobia, which in most respects metabolically resemble uninoculated plants, indicating a strong interdependency between N-fixation and S-assimilation.

A piscine birnavirus induces inhibition of protein synthesis in CHSE-214 cells primarily through the induction of eIF2α phosphorylation.

Inhibition of protein synthesis represents one of the antiviral mechanisms employed by cells and it is also used by viruses for their own propagation. To what extent members of the Birnaviridae family employ such strategies is not well understood. Here we use a type-strain of the Aquabirnavirus, infectious pancreatic necrosis virus (IPNV), to investigate this phenomenon in vitro. CHSE-214 cells were infected with IPNV and at 3, 12, 24, and 48 hours post infection (hpi) before the cells were harvested and labeled with S35 methionine to assess protein synthesis. eIF2α phosphorylation was examined by Western blot while RT-qPCR was used to assess virus replication and the expression levels of IFN-α, Mx1 and PKR. Cellular responses to IPNV infection were assessed by DNA laddering, Caspase-3 assays and flow cytometry. The results show that the onset and kinetics of eIF2α phosphorylation was similar to that of protein synthesis inhibition as shown by metabolic labeling. Increased virus replication and virus protein formation was observed by 12 hpi, peaking at 24 hpi. Apoptosis was induced in a small fraction (1-2%) of IPNV-infected CHSE cells from 24 hpi while necrotic/late apoptotic cells increased from 10% by 24 hpi to 59% at 48 hpi, as shown by flow cytometry. These results were in accordance with a small decline in cell viability by 24hpi, dropping below 50% by 48 hpi. IPNV induced IFN-α mRNA upregulation by 24 hpi while no change was observed in the expression of Mx1 and PKR mRNA. Collectively, these findings show that IPNV induces inhibition of protein synthesis in CHSE cells through phosphorylation of eIF2α with minimal involvement of apoptosis. The anticipation is that protein inhibition is used by the virus to evade the host innate antiviral responses.

Preparation of isotope-enriched heparan sulfate precursors for structural biology studies.

Heparan sulfate (HS) plays numerous important roles in biological systems through their interactions with a wide array of proteins. Structural biology studies of heparan sulfate are often challenging due to the heterogeneity and complexity of the HS molecules. Radioisotope metabolic labeling of HS in cellular systems has enabled the elucidation of HS structures as well as the interactions between HS and proteins. However, radiolabeled structures are not amenable for advanced structural glycobiology studies using sophisticated instruments such as nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). The utilization of stable isotope-enriched HS precursors is an appealing approach to overcome these challenges. The application of stable isotope-enriched HS precursors has facilitated the HS structural analysis by NMR spectroscopy and mass spectrometry. Herein we describe a simple method to prepare isotopically enriched HS precursors.

In vivo [35S]-methionine incorporation.

The purpose of this assay is to measure the incorporation of radiolabeled [(35)S]-methionine into newly synthesized proteins in exponentially growing yeast cells. This allows for a quantitative in vivo measurement of total protein synthesis.