Precursor Of Proline Research Articles

Arabidopsis thaliana argininosuccinate lyase structure uncovers the role of serine as the catalytic base

Arginine is an important amino acid in plants, as it not only plays a structural role and serves as nitrogen storage but is also a precursor for various molecules, including polyamines and proline. Arginine is produced by argininosuccinate lyase (ASL) which catalyzes the cleavage of argininosuccinate to arginine and fumarate. ASL belongs to the fumarate lyase family and while many members of this family were well-characterized, little is known about plant ASLs. Here we present the first crystal structures of ASL from the model plant, Arabidopsis thaliana (AtASL). One of the structures represents the unliganded form of the AtASL homotetramer. The other structure, obtained from a crystal soaked in argininosuccinate, accommodates the substrate or the reaction products in one of four active sites of the AtASL tetramer. Each active site is located at the interface of three neighboring protomers. The AtASL structure with ligands allowed us to analyze the enzyme-substrate and the enzyme-product interactions in detail. Furthermore, based on our analyses, we describe residues of AtASL crucial for catalysis. The structure of AtASL gives the rationale for the open-to-close transition of the GSS mobile loop and indicates the importance of serine 333 from this loop for the enzymatic action of the enzyme. Finally, we supplemented the structural data with the identification of sequence motifs characteristic for ASLs.

P5C as an Interface of Proline Interconvertible Amino Acids and Its Role in Regulation of Cell Survival and Apoptosis.

Studies of cancer metabolism have focused on the production of energy and the interconversion of carbons between cell cycles. More recently, amino acid metabolism, especially non-essential amino acids (NEAAs), has been investigated, underlining their regulatory role. One of the important mediators in energy production and interconversion of carbons in the cell is Δ1-pyrroline-5-carboxylate (P5C)—the physiological intracellular intermediate of the interconversion of proline, ornithine, and glutamate. As a central component of these conversions, it links the tricarboxylic acid cycle (TCA), urea cycle (UC), and proline cycle (PC). P5C has a cyclic structure containing a tertiary nitrogen atom (N) and is in tautomeric equilibrium with the open-chain form of L-glutamate-γ-semialdehyde (GSAL). P5C is produced by P5C synthase (P5CS) from glutamate, and ornithine via ornithine δ-amino acid transferase (δOAT). It can also be converted to glutamate by P5C dehydrogenase (P5CDH). P5C is both a direct precursor of proline and a product of its degradation. The conversion of P5C to proline is catalyzed by P5C reductase (PYCR), while proline to P5C by proline dehydrogenase/oxidase (PRODH/POX). P5C-proline-P5C interconversion forms a functional redox couple. Their transformations are accompanied by the transfer of a reducing-oxidizing potential, that affect the NADP+/NADPH ratio and a wide variety of processes, e.g., the synthesis of phosphoribosyl pyrophosphate (PRPP), and purine ribonucleotides, which are crucial for DNA synthesis. This review focuses on the metabolism of P5C in the cell as an interconversion mediator of proline, glutamate, and ornithine and its role in the regulation of survival and death with particular emphasis on the metabolic context.

Exogenous arginine enhances the chilling tolerance in postharvest papaya fruit by regulating arginine and proline metabolism

Papaya fruit is easily affected by low temperature, causing chilling injury (CI). In this study, the exogenous arginine was applied in the storage of postharvest papaya fruit and it was found that 0.8 mM arginine treatment significantly alleviated CI of papaya fruit. Arginine treatment promoted the accumulation of polyamines (PAs), which might be ascribed to the increased activities of arginase, arginine decarboxylase (ADC), ornithine decarboxylase (ODC), and S-adenosylmethionine decarboxylase (SAMDC). A higher accumulation of proline was found in arginine-treated papaya fruit, which may be due to increased activity of ornithine-δ-aminotransferase (OAT) and Δ1-pyrroline-5-carboxylate acid synthase (P5CS) and inhibited activity of proline dehydrogenase (PDH). In addition, arginine treatment increased higher nitric oxide synthase (NOS) activity and promoted the generation of nitric oxide (NO). The results of this study indicate that exogenous arginine may improve the chilling tolerance of postharvest papaya fruit by regulating arginine and proline metabolism. Practical applications In recent years, chilling injury of tropical fruits is a significant problem, including papaya. Many studies on polyamine, proline, nitric oxide, and chilling injury of fruits, but arginine, as a common precursor of polyamine, proline, and nitric oxide, are rarely studied, especially in papaya fruit. Our findings demonstrated that the exogenous arginine can regulate endogenous arginine metabolism, induce polyamine, putrescine, and nitric oxide accumulation, and coordinate to alleviate chilling injury of papaya fruit.

SYNTHON CHEMISTRY: THEORETICAL STUDY ON THE FORMATION OF PROLINE, PHENYLANALINE AND TYROSINE

According to the synthon theory on the formation of the first proteinogenic amino acids from three synthons: methylene, nitrene and carbon monoxide, at low temperatures, aziridinone would have formed. This, in contact with the same three synthons, forms the precursors of the 20 proteinogenic amino acids. These precursors, on contact with the components of the primary atmosphere, formed the first proteinogenic amino acids. The aim of this paper is to find the interradical reactions, which would have formed the precursors of proline, phenylalanine and tyrosine. The paper is a continuation of other studies on obtaining these amino acids in order to correlate them with their essential and non-essential character. As procedure, the quantitative results: enthalpies of formation, enthalpies of reaction, free energies, profile of reaction pathways were obtained by DFT calculations (B88-LYP).

Abscisic acid mediated proline biosynthesis and antioxidant ability in roots of two different rice genotypes under hypoxic stress

BackgroundAbscisic acid (ABA) and proline play important roles in rice acclimation to different stress conditions. To study whether cross-talk exists between ABA and proline, their roles in rice acclimation to hypoxia, rice growth, root oxidative damage and endogenous ABA and proline accumulation were investigated in two different rice genotypes (‘Nipponbare’ (Nip) and ‘Upland 502’ (U502)).ResultsCompared with U502 seedlings, Nip seedlings were highly tolerant to hypoxic stress, with increased plant biomass and leaf photosynthesis and decreased root oxidative damage. Hypoxia significantly stimulated the accumulation of proline and ABA in the roots of both cultivars, with a higher ABA level observed in Nip than in U502, whereas the proline levels showed no significant difference in the two cultivars. The time course variation showed that the root ABA and proline contents under hypoxia increased 1.5- and 1.2-fold in Nip, and 2.2- and 0.7-fold in U502, respectively, within the 1 d of hypoxic stress, but peak ABA production (1 d) occurred before proline accumulation (5 d) in both cultivars. Treatment with an ABA synthesis inhibitor (norflurazon, Norf) inhibited proline synthesis and simultaneously aggravated hypoxia-induced oxidative damage in the roots of both cultivars, but these effects were reversed by exogenous ABA application. Hypoxia plus Norf treatment also induced an increase in glutamate (the main precursor of proline). This indicates that proline accumulation is regulated by ABA-dependent signals under hypoxic stress. Moreover, genes involved in proline metabolism were differentially expressed between the two genotypes, with expression mediated by ABA under hypoxic stress. In Nip, hypoxia-induced proline accumulation in roots was attributed to the upregulation of OsP5CS2 and downregulation of OsProDH, whereas upregulation of OsP5CS1 combined with downregulation of OsProDH enhanced the proline level in U502.ConclusionThese results suggest that the high tolerance of the Nip cultivar is related to the high ABA level and ABA-mediated antioxidant capacity in roots. ABA acts upstream of proline accumulation by regulating the expression of genes encoding the key enzymes in proline biosynthesis, which also partly improves rice acclimation to hypoxic stress. However, other signaling pathways enhancing tolerance to hypoxia in the Nip cultivar still need to be elucidated.

Proline Precursors and Collagen Synthesis: Biochemical Challenges of Nutrient Supplementation and Wound Healing

Wound healing is a complex process marked by highly coordinated immune fluxes into an area of tissue injury; these are required for re-establishment of normal tissue integrity. Along with this cascade of cellular players, wound healing also requires coordinated flux through a number of biochemical pathways, leading to synthesis of collagen and recycling or removal of damaged tissues. The availability of nutrients, especially amino acids, is critical for wound healing, and enteral supplementation has been intensely studied as a potential mechanism to augment wound healing-either by increasing tensile strength, decreasing healing time, or both. From a practical standpoint, although enteral nutrient supplementation may seem like a reasonable strategy to augment healing, a number of biochemical and physiologic barriers exist that limit this strategy. In this critical review, the physiology of enteral amino acid metabolism and supplementation and challenges therein are discussed in the context of splanchnic physiology and biochemistry. Additionally, a review of studies examining various methods of amino acid supplementation and the associated effects on wound outcomes are discussed.

Tumour-specific proline vulnerability uncovered by differential ribosome codon reading.

Tumour growth and metabolic adaptation may restrict the availability of certain amino acids for protein synthesis. It has recently been shown that certain types of cancer cells depend on glycine, glutamine, leucine and serine metabolism to proliferate and survive. In addition, successful therapies using L-asparaginase-induced asparagine deprivation have been developed for acute lymphoblastic leukaemia. However, a tailored detection system for measuring restrictive amino acids in each tumour is currently not available. Here we harness ribosome profiling for sensing restrictive amino acids, and develop diricore, a procedure for differential ribosome measurements of codon reading. We first demonstrate the functionality and constraints of diricore using metabolic inhibitors and nutrient deprivation assays. Notably, treatment with L-asparaginase elicited both specific diricore signals at asparagine codons and high levels of asparagine synthetase (ASNS). We then applied diricore to kidney cancer and discover signals indicating restrictive proline. As for asparagine, this observation was linked to high levels of PYCR1, a key enzyme in proline production, suggesting a compensatory mechanism allowing tumour expansion. Indeed, PYCR1 is induced by shortage of proline precursors, and its suppression attenuated kidney cancer cell proliferation when proline was limiting. High PYCR1 is frequently observed in invasive breast carcinoma. In an in vivo model system of this tumour, we also uncover signals indicating restrictive proline. We further show that CRISPR-mediated knockout of PYCR1 impedes tumorigenic growth in this system. Thus, diricore has the potential to reveal unknown amino acid deficiencies, vulnerabilities that can be used to target key metabolic pathways for cancer treatment.

Mechanisms of induced susceptibility to Diplodia tip blight in drought-stressed Austrian pine.

Plants experiencing drought stress are frequently more susceptible to pathogens, likely via alterations in physiology that create favorable conditions for pathogens. Common plant responses to drought include the production of reactive oxygen species (ROS) and the accumulation of free amino acids (AAs), particularly proline. These same phenomena also frequently occur during pathogenic attack. Therefore, drought-induced perturbations in AA and ROS metabolism could potentially contribute to the observed enhanced susceptibility. Furthermore, nitrogen (N) availability can influence AA accumulation and affect plant resistance, but its contributions to drought-induced susceptibility are largely unexplored. Here we show that drought induces accumulation of hydrogen peroxide (H2O2) in Austrian pine (Pinus nigra Arnold) shoots, but that shoot infection by the blight and canker pathogen Diplodia sapinea (Fr.) Fuckel leads to large reductions in H2O2 levels in droughted plants. In in vitro assays, H2O2 was toxic to D. sapinea, and the fungus responded to this oxidative stress by increasing catalase and peroxidase activities, resulting in substantial H2O2 degradation. Proline increased in response to drought and infection when examined independently, but unlike all other AAs, proline further increased in infected shoots of droughted trees. In the same tissues, the proline precursor, glutamate, decreased significantly. Proline was found to protect D. sapinea from H2O2 damage, while also serving as a preferred N source in vitro. Fertilization increased constitutive and drought-induced levels of some AAs, but did not affect plant resistance. A new model integrating interactions of proline and H2O2 metabolism with drought and fungal infection of plants is proposed.

Uptake of amino acids and their metabolic conversion into the compatible solute proline confers osmoprotection to Bacillus subtilis.

The data presented here reveal a new facet of the physiological adjustment processes through which Bacillus subtilis can derive osmostress protection. We found that the import of proteogenic (Glu, Gln, Asp, Asn, and Arg) and of nonproteogenic (Orn and Cit) amino acids and their metabolic conversion into proline enhances growth under otherwise osmotically unfavorable conditions. Osmoprotection by amino acids depends on the functioning of the ProJ-ProA-ProH enzymes, but different entry points into this biosynthetic route are used by different amino acids to finally yield the compatible solute proline. Glu, Gln, Asp, and Asn are used to replenish the cellular pool of glutamate, the precursor for proline production, whereas Arg, Orn, and Cit are converted into γ-glutamic semialdehyde/Δ(1)-pyrroline-5-carboxylate, an intermediate in proline biosynthesis. The import of Glu, Gln, Asp, Asn, Arg, Orn, and Cit did not lead to a further increase in the size of the proline pool that is already present in osmotically stressed cells. Hence, our data suggest that osmoprotection of B. subtilis by this group of amino acids rests on the savings in biosynthetic building blocks and energy that would otherwise have to be devoted either to the synthesis of the proline precursor glutamate or of proline itself. Since glutamate is the direct biosynthetic precursor for proline, we studied its uptake and found that GltT, an Na(+)-coupled symporter, is the main uptake system for both glutamate and aspartate in B. subtilis. Collectively, our data show how effectively B. subtilis can exploit environmental resources to derive osmotic-stress protection through physiological means.

Adaptation of Bacillus subtilis carbon core metabolism to simultaneous nutrient limitation and osmotic challenge: a multi‐omics perspective

SummaryThe Gram‐positive bacterium Bacillus subtilis encounters nutrient limitations and osmotic stress in its natural soil ecosystem. To ensure survival and sustain growth, highly integrated adaptive responses are required. Here, we investigated the system‐wide response of B. subtilis to different, simultaneously imposed stresses. To address the anticipated complexity of the cellular response networks, we combined chemostat experiments under conditions of carbon limitation, salt stress and osmoprotection with multi‐omics analyses of the transcriptome, proteome, metabolome and fluxome. Surprisingly, the flux through central carbon and energy metabolism is very robust under all conditions studied. The key to achieve this robustness is the adjustment of the biocatalytic machinery to compensate for solvent‐induced impairment of enzymatic activities during osmotic stress. Specifically, increased production of several enzymes of central carbon metabolism compensates for their reduced activity in the presence of high salt. A major response of the cell during osmotic stress is the production of the compatible solute proline. This is achieved through the concerted adjustment of multiple reactions around the 2‐oxoglutarate node, which drives metabolism towards the proline precursor glutamate. The fine‐tuning of the transcriptional and metabolic networks involves functional modules that overarch the individual pathways.

Deacetylation of C/EBPβ is required for IL‐4‐induced arginase‐1 expression in murine macrophages

The amount of arginine available at inflammatory loci is a limiting factor for the growth of several cells of the immune system. IL-4-induced activation of macrophages produced arginase-1, which converts arginine into ornithine, a precursor of polyamines and proline. Trichostatin A (TSA), a pan-inhibitor of histone deacetylases (HDACs), inhibited IL-4-induced arginase-1 expression. TSA showed promoter-specific effects on the IL-4-responsive genes. While TSA inhibited the expression of arginase-1, fizz1, and mrc1, other genes, such as ym,1 mgl1, and mgl2, were not affected. The inhibition of arginase-1 occurred at the transcriptional level with the inhibition of polymerase II binding to the promoter. IL-4 induced STAT6 phosphorylation and binding to DNA. These activities were not affected by TSA treatment. However, TSA inhibited C/EBPβ DNA binding. This inhibitor induced acetylation on lysine residues 215-216, which are critical for DNA binding. Finally, using macrophages from STAT6 KO mice we showed that STAT6 is required for the DNA binding of C/EBPβ. These results demonstrate that the acetylation/deacetylation balance strongly influences the expression of arginase-1, a gene of alternative activation of macrophages. These findings also provide a molecular mechanism to explain the control of gene expression through deacetylase activity.

ROLE OF MATERNAL ERYTHROCYTE ARGINASE ACTIVITY IN PREGNANCY – A PILOT STUDY

Abstract Introduction Arginase is an urea cycle enzyme which catalyzes the cleavage of L arginine to L- ornithine and urea. It is expressed in liver, erythrocyte, brain, kidney, mammary gland and intestine. The arginase activity detected in nonhepatic tissues that lacka complete set of urea cycle enzymes is thought to provide ornithine, the biosynthetic precursor of proline, an important constituent of collagen, andthe polyamines, which are important for cell proliferation. Aim and objectives In the current study arginase level in maternal erythrocytes were determined to ascertain any possible role in pregnancy. Study design The study group comprised of total 45 subjects including twenty non – pregnant women (mean age 31.0 ± 6.0 years) and twenty five pregnant women (mean age 29.6 ± 6.1 years) of gestational age between 28 – 38 weeks. Results We found a significant increase in the level of maternal erythrocyte arginase (p 0.05) in pregnant women when compared to non – pregnant women. Conclusion Our study suggests that the increased maternal erythrocyte arginase activity may have a role in fetal growth and development.

Elevation of free proline and proline-rich protein levels by simultaneous manipulations of proline biosynthesis and degradation in plants

Proline-rich proteins (PRP) are cell wall and plasma membrane-anchored factors involved in cell wall maintenance and its stress-induced fortification. Here we compare the synthesis of P5C as the proline (Pro) precursor in the cytosol and chloroplast by an introduced alien system and evaluate correlation between PRP synthesis and free Pro accumulation in plants. We developed a Pro over-producing system by generating transgenic tobacco plants overexpressing E. coli P5C biosynthetic enzymes; Pro-indifferent gamma-glutamyl kinase 74 (GK74) and gamma-glutamylphosphate reductase (GPR), as well as antisensing proline dehydrogenase ( ProDH) transcription. GK74 and GPR enzymes were targeted either to the cytosol or plastids. Molecular analyses indicated that the two bacterial enzymes are efficiently expressed in plant cells, correctly targeted to the cytosol or chloroplasts, and processed to active enzymatic complexes in the two compartments. Maximal Pro increase is obtained when GK74 and GPR are active in chloroplasts, and ProDH mRNA level is reduced by anti-sense silencing, resulting in more than 50-fold higher Pro content compared to that of wild type tobacco plants. The Pro over-producing system efficiently works in tobacco and Arabidopsis. The elevation of Pro levels promotes accumulation of ectopically expressed Cell Wall Linker Protein (AtCWLP), a membrane protein with an external Pro-rich domain. These results suggest that the Pro-generating system can support endogenous or alien PRP production in plants.

Prevention of Amino Acid Conversion in SILAC Experiments with Embryonic Stem Cells

Recent studies using stable isotope labeling with amino acids in culture (SILAC) in quantitative proteomics have made mention of the problematic conversion of isotope-coded arginine to proline in cells. The resulting converted proline peptide divides the heavy peptide ion signal causing inaccuracy when compared with the light peptide ion signal. This is of particular concern as it can effect up to half of all peptides in a proteomic experiment. Strategies to both compensate for and limit the inadvertent conversion have been demonstrated, but none have been shown to prevent it. Additionally, these methods combined with SILAC labeling in general have proven problematic in their large scale application to sensitive cell types including embryonic stem cells (ESCs) from the mouse and human. Here, we show that by providing as little as 200 mg/liter L-proline in SILAC media, the conversion of arginine to proline can be rendered completely undetectable. At the same time, there was no compromise in labeling with isotope-coded arginine, indicating there is no observable back conversion from the proline supplement. As a result, when supplemented with proline, correct interpretation of "light" and "heavy" peptide ratios could be achieved even in the worst cases of conversion. By extending these principles to ESC culture protocols and reagents we were able to routinely SILAC label both mouse and human ESCs in the absence of feeder cells and without compromising the pluripotent phenotype. This study provides the simplest protocol to prevent proline artifacts in SILAC labeling experiments with arginine. Moreover, it presents a robust, feeder cell-free, protocol for performing SILAC experiments on ESCs from both the mouse and the human.

Functional role and species-specific contribution of arginases in pulmonary fibrosis

Lung fibrosis is characterized by increased deposition of ECM, especially collagens, and enhanced proliferation of fibroblasts. l-arginine is a key precursor of nitric oxide, asymmetric dimethylarginine, and proline, an amino acid enriched in collagen. We hypothesized that l-arginine metabolism is altered in pulmonary fibrosis, ultimately affecting collagen synthesis. Expression analysis of key enzymes in the arginine pathway, protein arginine methyltransferases (Prmt), arginine transporters, and arginases by quantitative (q) RT-PCR and Western blot revealed significant upregulation of arginase-1 and -2, but not Prmt or arginine transporters, during bleomycin-induced pulmonary fibrosis in mice. HPLC revealed a concomitant, time-dependent decrease in pulmonary l-arginine levels. Arginase-1 and -2 mRNA and protein expression was increased in primary fibroblasts isolated from bleomycin-treated mice, compared with controls, and assessed by qRT-PCR and Western blot analysis. TGF-beta1, a key profibrotic mediator, induced arginase-1 and -2 mRNA expression in primary and NIH/3T3 fibroblasts. Treatment of fibroblasts with the arginase inhibitor, NG-hydroxy-l-arginine, attenuated TGF-beta1-stimulated collagen deposition, but not collagen mRNA expression or Smad signaling, in fibroblasts. In human lungs derived from patients with idiopathic pulmonary fibrosis, arginase activity was unchanged, but arginase-1 expression significantly decreased when compared with donor lungs. Our results thus demonstrate that arginase-1 is expressed and functionally important for collagen deposition in lung fibroblasts. TGF-beta1-induced upregulation of arginase-1 suggests an interplay between profibrotic agents and l-arginine metabolism during the course of lung fibrosis in the mouse, whereas species-specific regulatory mechanisms may account for the differences observed in mouse and human.

Effect of Drought Stress at Supraoptimal Temperature on Polyamine Concentrations in Transgenic Soybean with Increased Proline Levels

The effect of drought stress at supraoptimal temperature on free proline and polyamine levels was compared in wild type and transgenic soybean (Glycine max cv. Ibis) plants having increased proline levels. Since glutamate and arginine are precursors of both proline and polyamines, it was assumed that the genetic manipulation of proline levels would also affect the polyamine levels. The proline and spermine concentrations increased, while the putrescine concentration generally decreased or did not change after the treatments in both genotypes. Following drought higher proline and lower spermine levels were detected in the transgenic plants compared to the wild type ones, which could be explained by the increased use of their common precursors for proline biosynthesis in the transgenic plants.

Glutamine synthetase and glutamate dehydrogenase contribute differentially to proline accumulation in leaves of wheat ( Triticum aestivum) seedlings exposed to different salinity

To investigate the roles of ammonium-assimilating enzymes in proline synthesis under salinity stress, the activities of glutamine synthetase (GS; EC 6.3.1.2) and NADH-dependent glutamate dehydrogenase (NADH-GDH; EC 1.4.1.2) were determined in leaves of wheat (Triticum aestivum) seedlings exposed to salt stress at 150 and 300 mM NaCl for 5d. At the lower salinity, only GS activity increased markedly. At 300 mM NaCl, however, NADH-GDH activity increased while GS activity decreased. A significant accumulation of proline was found only at high-salinity exposure while glutamate, a proline precursor, increased dramatically under both low and high salinity. These data suggests that GS-catalysis might be the main glutamate synthesis pathway under low salinity. At 300 mM NaCl, glutamate seems to be preferentially produced through the process catalyzed by NADH-GDH. The increase of ammonium in salinity-stressed wheat seedlings might have resulted from increased photorespiration, which is responsible for the higher NADH-GDH activity. The activity of Delta(1)-pyrroline-5-carboxylate reductase (P5CR; EC 1.5.1.2) was significantly enhanced at 300 mM NaCl but remained unchanged at 150 mM. Delta(1)-Pyrroline-5-carboxylate synthetase (P5CS) activity did not show a specific response, indicating that P5CR might be the limiting step in proline synthesis from glutamate at high salinity.

Salt stress adaptation of Bacillus subtilis: A physiological proteomics approach

The adaptation to osmotic stress is crucial for growth and survival of Bacillus subtilis in its natural ecosystem. Dual channel imaging and warping of 2-D protein gels were used to visualize global changes in the protein synthesis pattern of cells in response to osmotic stress (6% NaCl). Many vegetative enzymes were repressed in response to salt stress and derepressed after resumption of growth. The enzymes catalyzing the metabolic steps from glucose to 2-oxoglutarate, however, were almost constantly synthesized during salt stress despite the growth arrest. This indicates an enhanced need for the proline precursor glutamate. The synthesis of enzymes involved in sulfate assimilation and in the formation of Fe-S clusters was also induced, suggesting an enhanced need for the formation or repair of Fe-S clusters in response to salt stress. One of the most obvious changes in the protein synthesis profile can be followed by the very strong induction of the SigB regulon. Furthermore, members of the SigW regulon and of the PerR regulon, indicating oxidative stress after salt challenge, were also induced. This proteomic approach provides an overview of cell adaptation to an osmotic upshift in B. subtilis visualizing the most dramatic changes in the protein synthesis pattern.

Arginine/Arginase NO NO NO

Arginine is a semi-essential amino acid that plays a critical role in several metabolic pathways. The best known of these is as the immediate precursor of urea in the liver and to a lesser extent in the intestine.1 The enzyme responsible for the cleavage of arginine to produce urea is arginase, which is the only enzyme in the urea cycle that comes in two forms, arginase I, a cytosolic enzyme, and arginase II, a mitochondrial enzyme. These enzymes exist not only in the liver and intestine where urea is generated but are also widely distributed in the body. Ornithine, the other product of the cleavage of arginine by arginase, is a precursor of proline and polyamines such as spermine, spermidine, and putrescine. Arginine is also the precursor of nitric oxide (NO). See page 365 In an important article authored by Teupser and colleagues,2 arginase in macrophages has been identified as a candidate gene influencing atheroresponsiveness. They created and studied two strains of rabbits with genetically determined high (HAR) and low (LAR) atherosclerosis susceptibility. Subtractive suppression hybridization was used to screen for genes that were more highly expressed in macrophages from LAR rabbits. Among the 42 clones identified were four differentially expressed genes with potential relevance to atherogenesis. These were OC2 protein, fibronectin, ferritin H-chain, and arginase I. Despite their identification in the screen, the first three genes were not differentially expressed in macrophages between HAR and LAR animals when checked by quantitative RT-PCR. In contrast, arginase I was more highly expressed in LAR than HAR macrophages, and its expression level was correlated with higher arginase enzymatic activity. They further identified a length polymorphism of the mRNA for arginase I that was attributable to the presence (long variant) or absence (short variant) of a 413-bp C repeat in the …

Proline Accumulation Induced by Phosphinothricin in Rice Leaves

The effect phosphinothricin (PPT), an inhibitor of glutamine synthetase (GS), on proline accumulation in detached rice leaves was investigated. During 12 h incubation, PPT inhibited GS activity and induced accumulation of NH4 +, and accumulation of proline in the light but not in darkness. Proline accumulation caused by PPT in the light was related to protein hydrolysis, and increase in the contents of precursors of proline, ornithine and arginine. Abscisic acid accumulation was not required for proline accumulation in PPT-treated rice leaves.