Responsible Enzyme Research Articles

The glucosyltransferase Xiantuan of the endoplasmic reticulum specifically affects E-Cadherin expression and is required for gastrulation movements in Drosophila

The majority of membrane and secreted proteins, including many developmentally important signalling proteins, receptors and adhesion molecules, are cotranslationally N-glycosylated in the endoplasmic reticulum. The structure of the N-glycan is invariant for all substrates and conserved in eukaryotes. Correspondingly, the enzymes are conserved, which successively assemble the glycan precursor from activated monosaccharides prior to transfer to nascent proteins. Despite the well-defined biochemistry, the physiological and developmental role of N-glycosylation and of the responsible enzymes has not been much investigated in metazoa. We identified a mutation in the Drosophila gene, xiantuan (xit, CG4542), which encodes one of the conserved enzymes involved in addition of the terminal glucose residues to the glycan precursor. xit is required for timely apical constriction of mesoderm precursor cells and ventral furrow formation in early embryogenesis. Furthermore, cell intercalation in the lateral epidermis during germband extension is impaired in xit mutants. xit affects glycosylation and intracellular distribution of E-Cadherin, albeit not the total amount of E-Cadherin protein. As depletion of E-Cadherin by RNAi induces a similar cell intercalation defect, E-Cadherin may be the major xit target that is functionally relevant for germband extension.

Degradation of polyurethane by bacterium isolated from soil and assessment of polyurethanolytic activity of a Pseudomonas putida strain

The increasing usage and the persistence of polyester polyurethane (PU) generate significant sources of environmental pollution. The effective and environmental friendly bioremediation techniques for this refractory waste are in high demand. In this study, three novel PU degrading bacteria were isolated from farm soils and activated sludge. Based upon 16S ribosomal RNA gene sequence blast, their identities were determined. Particularly robust activity was observed in Pseudomonas putida; it spent 4 days to degrade 92% of Impranil DLN(TM) for supporting its growth. The optimum temperature and pH for DLN removal by P. putida were 25 °C and 8.4, respectively. The degradation and transformation of DLN investigated by Fourier transformed infrared spectroscopy show the decrease in ester functional group and the emergence of amide group. The polyurethanolytic activities were both presented in the extracellular fraction and in the cytosol. Esterase activity was detected in the cell lysate. A 45-kDa protein bearing polyurethanolytic activity was also detected in the extracellular medium. This study presented high PU degrading activity of P. putida and demonstrated its responsible enzymes during the PU degradation process, which could be applied in the bioremediation and management of plastic wastes.

Oxalate-metabolising genes of the white-rot fungus Dichomitus squalens are differentially induced on wood and at high proton concentration.

Oxalic acid is a prevalent fungal metabolite with versatile roles in growth and nutrition, including degradation of plant biomass. However, the toxicity of oxalic acid makes regulation of its intra- and extracellular concentration crucial. To increase the knowledge of fungal oxalate metabolism, a transcriptional level study on oxalate-catabolising genes was performed with an effective lignin-degrading white-rot fungus Dichomitus squalens, which has demonstrated particular abilities in production and degradation of oxalic acid. The expression of oxalic-acid decomposing oxalate decarboxylase (ODC) and formic-acid decomposing formate dehydrogenase (FDH) encoding genes was followed during the growth of D. squalens on its natural spruce wood substrate. The effect of high proton concentration on the regulation of the oxalate-catabolising genes was determined after addition of organic acid (oxalic acid) and inorganic acid (hydrochloric acid) to the liquid cultures of D. squalens. In order to evaluate the co-expression of oxalate-catabolising and manganese peroxidase (MnP) encoding genes, the expression of one MnP encoding gene, mnp1, of D. squalens was also surveyed in the solid state and liquid cultures. Sequential action of ODC and FDH encoding genes was detected in the studied cultivations. The odc1, fdh2 and fdh3 genes of D. squalens showed constitutive expression, whereas ODC2 and FHD1 most likely are the main responsible enzymes for detoxification of high concentrations of oxalic and formic acids. The results also confirmed the central role of ODC1 when D. squalens grows on coniferous wood. Phylogenetic analysis revealed that fungal ODCs have evolved from at least two gene copies whereas FDHs have a single ancestral gene. As a conclusion, the multiplicity of oxalate-catabolising genes and their differential regulation on wood and in acid-amended cultures of D. squalens point to divergent physiological roles for the corresponding enzymes.

Getting CAD in Shape: The Atomic Structure of Human Dihydroorotase Domain

CAD is a large multifunctional polypeptide that initiates and controls the de novo biosynthesis of pyrimidines in animals. In this issue of Structure, Grande-García and colleagues provide the first atomic information of this antitumoral target by reporting the crystal structure of the dihydroorotase domain of human CAD.

Remodeling of glycans using glycosyltransferase genes.

Remodeling of glycans on the cell surface is an essential technique to analyze cellular function of lectin-glycan ligand interaction. Here we describe the methods to identify the responsible enzyme (glycosyltransferase) regulating the expression of the glycan of interest and to modulate the glycan expression by overexpressing the glycosyltransferase gene. For the identification of the responsible enzyme, we introduce a new method, CIRES (correlation index-based responsible-enzyme gene screening), that consists of statistical comparison of glycan expression profile obtained by flow cytometry and gene expression profile obtained by DNA microarray.

Glycosylation changes leading to the increase in size on the common core of N-glycans, required enzymes, and related cancer-associated proteins

Glycan parts of glycoconjugates on the surfaces of cells regulate many kinds of interactions between the cells and their immediate environments. Alterations in glycosylation on the cancer-associated glycoproteins are responsible for changes in their molecular interactions and biological functions. Glycosylation changes occur in the core and/or at the nonreducing end of the oligosaccharide chains of N-glycans. In this review, we focus on the branching of the common core structure of N-glycans, the responsible enzyme, and the extensions of some of the branches causing size increases on the surface of tumor cells. Abnormal branching, elongation of the branches, and increasing size of the common core of N-glycans are the typical features of these changes and are related with malignant transformations. Seven N-acetylglucosaminyltransferases (GnTs) (GnT-I, GnT-II, GnT-III, GnT-IV, GnT-V, GnT-VI, and GnT-IX) and alpha\1,6-fucosyltransferase (FUT8) initiate the new branches on the core. GnT-IV, GnT-V, and GnT-IX initiate the branches available for poly-LacNAc extensions, which are responsible for tumor progression and metastasis. GnT-III prevents the catalytic activity of GnT-II, GnT-IV, GnT-V, and FUT8 to form branching and elongation of the branches. The contributions of GnT-III and the other enzymes to the cancer progression are in conflict with each other. While GnT-III prevents cancer, the others increase metastasis. The function of FUT8 is related to signal transduction and its activity is higher in tumor tissue than in healthy tissue. The impact of glycosylation changes on some of the cancer-associated proteins (growth factor receptors, adhesion and signal molecules, CD147, TIMP-1, and matriptase) is also summarized.

Main Metabolic Pathways of TAK-802, a Novel Drug Candidate for Voiding Dysfunction, in Humans: The Involvement of Carbonyl Reduction by 11β-hydroxysteroid Dehydrogenase 1

To investigate species differences in the metabolism of TAK-802, in vitro and in vivo metabolic profiles were compared between humans and animals. TAK-802 was mainly metabolized to M-I, M-II, M-III and M-IV in human and animal liver microsomes. Especially the M-IV formation in humans was greater than that in animals. Likewise, M-IV was detected to a lower extent in the plasma and excreta of animals administered with TAK-802, whereas the AUC0-48 h of M-IV was approximately five-fold higher than that of TAK-802 in human plasma. These results indicate that the in vitro metabolic profile reflects the in vivo condition. Thus, to identify the metabolic pathway of TAK-802 in humans, the responsible enzyme to form M-IV was elucidated in vitro. Since M-IV is a reductive metabolite formed in microsomes, the possibility of involvement of 11β-hydroxysteroid dehydrogenase (11β-HSD), a carbonyl reductase located in microsomes, was first investigated. Consequently, M-IV formation was confirmed by incubation with human 11β-HSD1-expressing microsomes and was concentration-dependently inhibited by glycyrrhetinic acid, an inhibitor for 11β-HSD enzymes, indicating the involvement of 11β-HSD1 in the M-IV formation. In contrast, little M-IV formation was observed using rat 11β-HSD1, suggesting species differences between humans and rats. In addition, M-II was formed via M-IV, not via M-I and the CYP identification studies revealed that both M-I formation from TAK-802 and M-II formation from M-IV were mainly catalyzed by CYP3A4. In conclusion, 11β-HSD1 and CYP3A4 are principally responsible for the metabolism of TAK-802 in humans and 11β-HSD1 may be responsible for the observed species difference.

Contribution of the 7β-hydroxysteroid dehydrogenase from Ruminococcus gnavus N53 to ursodeoxycholic acid formation in the human colon

Bile acid composition in the colon is determined by bile acid flow in the intestines, the population of bile acid-converting bacteria, and the properties of the responsible bacterial enzymes. Ursodeoxycholic acid (UDCA) is regarded as a chemopreventive beneficial bile acid due to its low hydrophobicity. However, it is a minor constituent of human bile acids. Here, we characterized an UDCA-producing bacterium, N53, isolated from human feces. 16S rDNA sequence analysis identified this isolate as Ruminococcus gnavus, a novel UDCA-producer. The forward reaction that produces UDCA from 7-oxo-lithocholic acid was observed to have a growth-dependent conversion rate of 90-100% after culture in GAM broth containing 1 mM 7-oxo-lithocholic acid, while the reverse reaction was undetectable. The gene encoding 7β-hydroxysteroid dehydrogenase (7β-HSDH), which facilitates the UDCA-producing reaction, was cloned and overexpressed in Escherichia coli. Characterization of the purified 7β-HSDH revealed that the kcat/Km value was about 55-fold higher for the forward reaction than for the reverse reaction, indicating that the enzyme favors the UDCA-producing reaction. As R. gnavus is a common, core bacterium of the human gut microbiota, these results suggest that this bacterium plays a pivotal role in UDCA formation in the colon.

Proteomics methods to study methionine oxidation

The oxidation and consequent reduction of protein-bound methionine residues is of great interest in understanding different aspects of how oxidative stress affects protein functions and cellular signaling. To date, few technologies are available for the study of methionine sulfoxides. And, especially the absence of highly specific antibodies has impeded the field in understanding the exact role of methionine oxidation on a proteome-wide level. Nonetheless, the different models where the responsible enzymes for repair of the oxidized methionines have been studied show that there is an important role for this modification in a cellular context. We here review different mass spectrometry based and proteomics methods for characterizing in vivo methionine oxidation.

CYP2R1 is a major, but not exclusive, contributor to 25-hydroxyvitamin D production in vivo

Bioactivation of vitamin D consists of two sequential hydroxylation steps to produce 1α,25-dihydroxyvitamin D3. It is clear that the second or 1α-hydroxylation step is carried out by a single enzyme, 25-hydroxyvitamin D 1α-hydroxylase CYP27B1. However, it is not certain what enzyme or enzymes are responsible for the initial 25-hydroxylation. An excellent case has been made for vitamin D 25-hydroxylase CYP2R1, but this hypothesis has not yet been tested. We have now produced Cyp2r1 (-/-) mice. These mice had greater than 50% reduction in serum 25-hydroxyvitamin D3. Curiously, the 1α,25-dihydroxyvitamin D3 level in the serum remained unchanged. These mice presented no health issues. A double knockout of Cyp2r1 and Cyp27a1 maintained a similar circulating level of 25-hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3. Our results support the idea that the CYP2R1 is the major enzyme responsible for 25-hydroxylation of vitamin D, but clearly a second, as-yet unknown, enzyme is another contributor to this important step in vitamin D activation.

Abstract 62: Novel role of Aminopeptidase A enzyme in Ang-(1-7) metabolism Post Myocardial Infarction

Aminopeptidase A (APA) is a metalloprotease that is activated in cardiovascular diseases. Ang-(1-7) has been shown to have beneficial effects in myocardial injury. The aims of this study are to (1) Test the role of APA in cardiac pathology using the myocardial infarction (MI) model, (2) Investigate the role of APA in Ang-(1-7) metabolism (3) Explore the effect of APA inhibition on Ang-(1-7) homeostasis. APA activity was measured using mass spectrometry (MS) based in vitro and in situ enzyme assays. For the in vitro assay, heart homogenates were incubated with 50 μM Ang II in assay buffer and for absolute quantitation stable-isotope labeled internal standards were added. In the in situ MS imaging, frozen myocardial sections were incubated with 100 μM Ang II for 10 min and the resultant peptides were assessed on the tissue sections. For kinetic studies and Km determination, recombinant APA was incubated with Ang II and Ang-(1-7) in concentrations ranging from 1-100 μM. Results from the in vitro MS enzyme assays showed that myocardial APA activity was significantly increased after 24 hrs MI compared to sham (Ang III=0.82±0.02 vs. 0.32± 0.02 ρmol/min/μg in MI vs sham, respectively, p<0.01). The in situ MS imaging results confirmed that Ang III intensity was higher in MI heart sections compared to sham (96325±214 for MI and 1041±75 AU for Sham, p<0.05). Both MS enzyme assays identified a new peptide Ang-(2-7), m/z 784, which accumulated in the MI compared to Sham (136.96± 6.5 vs 78.94±3 AU in MI and Sham, respectively, p<0.05). Inhibition of APA with 4-Amino-phosphono-butyric acid significantly decreased formation of Ang-(2-7) from Ang-(1-7) and Ang III from Ang II by 98± 0.7% and 82±2.6% (p<0.05), respectively, indicating that APA is the responsible enzyme for the myocardial formation of both peptides. Interestingly, APA exhibited a higher substrate affinity for Ang-(1-7) compared to Ang II (Km for Ang II=14.32±1.6 vs Km for Ang-(1-7) =6.34± 1.12 μM, p<0.05). In conclusion, we have shown for the first time that APA is responsible for Ang-(1-7) degradation to Ang-(2-7). An upregulation of this pathway in myocardial injury may deprive the heart of cardioprotective Ang-(1-7). Thus, APA can be a potentially novel therapeutic target for management of myocardial remodeling after MI.

Different Hydrolases Involved in Bioactivation of Prodrug-Type Angiotensin Receptor Blockers: Carboxymethylenebutenolidase and Carboxylesterase 1

Olmesartan medoxomil (OM) is a prodrug-type angiotensin II type 1 receptor blocker (ARB). We recently identified carboxymethylenebutenolidase homolog (CMBL) as the responsible enzyme for OM bioactivation in humans. In the present study, we compared the bioactivating properties of OM with those of other prodrug-type ARBs, candesartan cilexetil (CC) and azilsartan medoxomil (AM), by focusing on interspecies differences and tissue specificity. In in-vitro experiments with pooled tissue subcellular fractions of mice, rats, monkeys, dogs, and humans, substantial OM-hydrolase activities were observed in cytosols of the liver, intestine, and kidney in all the species tested except for dog intestine, which showed negligible activity, whereas lung cytosols showed relatively low activities compared with the other tissues. AM-hydrolase activities were well correlated with the OM-hydrolase activities. In contrast, liver microsomes exhibited the highest CC-hydrolase activity among various tissue subcellular fractions in all the species tested. As a result of Western blot analysis with the tissue subcellular fractions, the band intensities stained with anti-human CMBL and carboxylesterase 1 (CES1) antibodies well reflected OM- and AM-hydrolase activities and CC-hydrolase activity, respectively, in animals and humans. Recombinant human CMBL and CES1 showed significant AM- and CC-hydrolase activities, respectively, whereas CC hydrolysis was hardly catalyzed with recombinant carboxylesterase 2 (CES2). In conclusion, OM is bioactivated mainly via intestinal and additionally hepatic CMBL not only in humans but also in mice, rats, and monkeys, while CC is bioactivated via hepatic CES1 rather than intestinal enzymes, including CES2. AM is a substrate for CMBL.

Post-translation modification in Archaea: lessons fromHaloferax volcaniiand other haloarchaea

As an ever-growing number of genome sequences appear, it is becoming increasingly clear that factors other than genome sequence impart complexity to the proteome. Of the various sources of proteomic variability, post-translational modifications (PTMs) most greatly serve to expand the variety of proteins found in the cell. Likewise, modulating the rates at which different proteins are degraded also results in a constantly changing cellular protein profile. While both strategies for generating proteomic diversity are adopted by organisms across evolution, the responsible pathways and enzymes in Archaea are often less well described than are their eukaryotic and bacterial counterparts. Studies on halophilic archaea, in particular Haloferax volcanii, originally isolated from the Dead Sea, are helping to fill the void. In this review, recent developments concerning PTMs and protein degradation in the haloarchaea are discussed.

AB0181 Padi4 haplotype a potential modulator of antigen expression in an immunological environment

BackgroundPeptidil arginine deiminase IV (PAD 4) is the responsible enzyme for a posttranslational modification called citrullination, originating the antigenic determinant recognized by anti-cyclic citrullinated peptide antibodies (aCCP)1. Four SNPs (single...

Nondegradative Extraction and Measurement of Uric Acid from Poultry Litter

Due to limited solubility of uric acid from poultry litter (PL), alkaline solutions are frequently used to extract uric acid from PL for measurement, but the high pH can cause oxidation of the analyte. Our objective was to compare 0.1 M sodium acetate, 0.025 M Li2CO3, and a NaOH/Na2PO4 buffer as a means of extracting uric acid from PL for analysis by high‐pressure liquid chromatography (HPLC). In laboratory experiments, extractant‐induced degradation of reagent uric acid proceeded at a rate of 80 g kg−1 d−1 in 0.025 M of Li2CO3 (pH 11.2) and a NaOH/Na2PO4 buffer (pH 12.4) compared with no degradation in sodium acetate over a 2‐d period. In extracted PL samples, the alkaline extractants were found to enhance the enzymatic oxidation of uric acid to completion in Li2CO3 and by 800 g kg−1 in a NaOH/Na2PO4 buffer over the same 2‐d period. Sodium acetate extraction resulted in minimal loss of analyte (30 g kg−1), possibly due to thermal inactivation of the responsible enzyme uricase. Stabilization of the dissolved uric acid extracted from PL samples allowed for the development of a very accurate measurement procedure by HPLC with ultraviolet (UV)–visible light spectrometer (VIS) detection at 290 nm. Our results suggest a reporting limit of 8.5 mg uric acid–N kg−1 of litter. Of the 118 PL samples that were analyzed in this study, uric acid‐, ammonium‐, and nitrate‐N concentrations accounted for an average of 9.4, 17.4, and 1.2%, respectively, of the total N present in PL.

Cloning of Catechol 2,3-Dioxygenase Gene and Construction of a Stable Genetically Engineered Strain for Degrading Crude Oil

Pseudomonas putida strain BNF1 was isolated to degrade aromatic hydrocarbons efficiently and use phenol as a main carbon and energy source to support its growth. Catechol 2,3-dioxygenase was found to be the responsible key enzyme for the biodegradation of aromatic hydrocarbons. Catechol 2,3-dioxygenase gene was cloned from plasmid DNA of P. putida strain BNF1. The nucleotide base sequence of a 924bp segment encoding the catechol 2,3-dioxygenase (C23O) was determined. This segment showed an open reading frame, which encoded a polypeptide of 307 amino acids. C23O gene was inserted into NotI-cut transposon vector pUT/mini-Tn5 (Km(r)) to get a novel transposon vector pUT/mini-Tn5-C23O. With the helper plasmid PRK2013, the transposon vector pUT/mini-Tn5-C23O was introduced into one alkanes degrading strain Acinetobacter sp. BS3 by triparental conjugation, and then the C23O gene was integrated into the chromosome of Acinetobacter sp. BS3. And the recombinant BS3-C23O, which could express catechol 2,3-dioxygenase protein, was obtained. The recombinant BS3-C23O was able to degrade various aromatic hydrocarbons and n-alkanes. Broad substrate specificity, high enzyme activity, and the favorable stability suggest that the BS3-C23O was a potential candidate used for the biodegradation of crude oil.

Aspirin delays skin wound healing by reducing the production of 12‐hydroxyheptadecatrienoic acid, a ligand for BLT2 receptor

Aspirin, the most famous non steroidal anti‐inflammatory drug (NSAID), is widely used to kill pain and fever by inhibiting cyclooxygenases to produce prostaglandins (PGs). Aspirin is also famous for its serious side effects including mucosal damage of gastrointestinal tracts and delay in skin wound healing. Although reduced production of prostaglandins by aspirin is generally accepted as a common mechanism for these side effects, several reports using genetically engineered mice that lack PG production and PG receptors failed to prove the mechanism. We found that aspirin‐dependent reduction of 12‐hydroxyheptadecatrienoic acid (12‐HHT), an endogenous ligand for leukotriene B4 receptor type 2 (BLT2), is responsible for the delay in skin wound healing. Aspirin delayed the wound closure after skin punching in mice, which was completely abolished in BLT2‐deficient mice. Furthermore, mice deficient in BLT2 or thromboxane A2 synthase, a responsible enzyme for 12‐HHT production, exhibited delayed wound healing. 12‐HHT is produced during blood coagulation and activates BLT2 expressed in keratinocytes to release tumor necrosis factor α and metalloproteinases to induce keratinocyte migration. A synthetic BLT2 agonist accelerated wound closure in vitro and in C57BL/6J and db/db mice. Our results clarify the novel mechanism of aspirin actions, and BLT2 agonists are possible therapeutic drugs for wounds especially for diabetic ulcer.

Biotransformation of Two β-Secretase Inhibitors Including Ring Opening and Contraction of a Pyrimidine Ring

Recently, the discovery of the aminoisoindoles as potent and selective inhibitors of β-secretase was reported, including the close structural analogs compound (S)-1-pyridin-4-yl-4-fluoro-1-(3-(pyrimidin-5-yl)phenyl)-1H-isoindol-3-amine [(S)-25] and (S)-1-(2-(difluoromethyl)pyridin-4-yl)-4-fluoro-1-(3-(pyrimidin-5-yl)phenyl)-1H-isoindol-3-amine hemifumarate (AZD3839), the latter being recently progressed to the clinic. The biotransformation of (S)-25 was investigated in vitro and in vivo in rat, rabbit, and human and compared with AZD3839 to further understand the metabolic fate of these compounds. In vitro, CYP3A4 was the major responsible enzyme and metabolized both compounds to a large extent in the commonly shared pyridine and pyrimidine rings. The main proposed metabolic pathways in various in vitro systems were N-oxidation of the pyridine and/or pyrimidine ring and conversion to 4-pyrimidone and pyrimidine-2,4-dione. Both compounds were extensively metabolized, and more than 90% was excreted in feces after intravenous administration of radiolabeled compound to the rat. Here, the main pathways were N-oxidation of the pyridine and/or pyrimidine ring and a ring contraction of the pyrimidine ring into an imidazole ring. Ring-contracted metabolites accounted for 25% of the total metabolism in the rat for (S)-25, whereas the contribution was much smaller for AZD3839. This metabolic pathway was not foreseen on the basis of the obtained in vitro data. In conclusion, we discovered an unusual metabolic pathway of aryl-pyrimidine-containing compounds by a ring-opening reaction followed by elimination of a carbon atom and a ring closure to form an imidazole ring.

Growth and Cyanide Degradation of Azotobacter vinelandii in Cyanide-Containing Wastewater System

Azotobacter vinelandii, a strict aerobic nitrogen-fixing bacterium, has been extensively studied with regard to the ability of N2-fixation due to its high expression of nitrogenase and fast growth. Because nitrogenase can also reduce cyanide to ammonia and methane, cyanide degradation by A. vinelandii has been studied for the application in the bioremediation of cyanide-contaminated wastewater. Cyanide degradation by A. vinelandii in NFS (nitrogen-free sucrose) medium was examined in terms of cell growth and cyanide reduction, and the results were applied for cyanide-contaminated cassava mill wastewater. From the NFS medium study in the 300 ml flask, it was found that A. vinelandii in the early stationary growth phase could reduce cyanide more rapidly than the cells in the exponential growth phase, and 84.4% of cyanide was degraded in 66 h incubation upon addition of 3.0 mM of NaCN. The resting cells of A. vinelandii could also reduce cyanide concentration by 90.4% with 3.0 mM of NaCN in the large-scale (3 L) fermentation with the same incubation time. Finally, the optimized conditions were applied to the cassava mill wastewater bioremediation, and A. vinelandii was able to reduce the cyanide concentration by 69.7% after 66 h in the cassava mill wastewater containing 4.0 mM of NaCN in the 3 L fermenter. Related to cyanide degradation in the cassava mill wastewater, nitrogenase was the responsible enzyme, which was confirmed by methane production. These findings would be helpful to design a practical bioremediation system for the treatment of cyanide-contaminated wastewater.

Nucleotide degradation and ribose salvage in yeast

Nucleotide degradation is a universal metabolic capability. Here we combine metabolomics, genetics and biochemistry to characterize the yeast pathway. Nutrient starvation, via PKA, AMPK/SNF1, and TOR, triggers autophagic breakdown of ribosomes into nucleotides. A protein not previously associated with nucleotide degradation, Phm8, converts nucleotide monophosphates into nucleosides. Downstream steps, which involve the purine nucleoside phosphorylase, Pnp1, and pyrimidine nucleoside hydrolase, Urh1, funnel ribose into the nonoxidative pentose phosphate pathway. During carbon starvation, the ribose-derived carbon accumulates as sedoheptulose-7-phosphate, whose consumption by transaldolase is impaired due to depletion of transaldolase's other substrate, glyceraldehyde-3-phosphate. Oxidative stress increases glyceraldehyde-3-phosphate, resulting in rapid consumption of sedoheptulose-7-phosphate to make NADPH for antioxidant defense. Ablation of Phm8 or double deletion of Pnp1 and Urh1 prevent effective nucleotide salvage, resulting in metabolite depletion and impaired survival of starving yeast. Thus, ribose salvage provides means of surviving nutrient starvation and oxidative stress.