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Helicobacter pylori infection is the cause of 90% of non-cardia gastric cancer. Several dietary elements have been identified as possible contributors to H. pylori infection and its advancement through various pathways. Based on the anti-inflammatory and anti-microbial effects of a diet low in omega-6 and high in omega-3 polyunsaturated fatty acids (PUFAs), this study aimed to assess the ratio of dietary omega-6 to omega-3 PUFAs and the risk of developing H. pylori. The present case-control study was conducted on 150 cases with H. pylori infection and 302 controls. The omega-6 to omega-3 ratio was calculated using food intake information sourced from a validated food frequency questionnaire. Physical activity and demographic data were collected through a related questionnaire. The association between the odds of H. pylori infection and the omega-6 to omega-3 ratio was evaluated using logistic regression models. A p value < 0.05 was considered statistically significant. The findings revealed that individuals in the third tertile had significantly higher odds of H. pylori (odds ratio [OR], 2.10; 95% confidence interval [CI], 1.30-3.40) in the crude model. Furthermore, even after adjusting the potential confounders including sex, age, body mass index, physical activity, energy intake, alcohol, and smoking status, this association remained significant (fully adjusted model: OR, 2.00; 95% CI, 1.17-3.34). Our study revealed a higher ratio of omega-6 to omega-3 was related to a higher likelihood of H. pylori infection. Therefore, it is advisable to maintain a balanced intake of PUFAs in the diet.
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The components in our food are known as one of the important risk factors for the development of Helicobacter pylori (H. pylori) infection. A balanced diet, rich in fruits and vegetables, and free of fat, sugar, and salt, might protect people from the consequences of H. pylori infection. Therefore, the purpose of this study was to investigate the associations between ultra-processed foods (UPFs) intake and the risk of H. pylori infection. The case-control study was conducted to assess the intake of UPFs in patients with H. pylori infection compared with healthy individuals. The dietary data of the contributors were collected by a validated food frequency questionnaire (FFQ). To estimate the UPFs intake, the classification of the NOVA food group was utilized. The associations of intake UPFs with H. pylori infection were assessed using binary logistic regression. Finally, dietary data of 150 cases and 302 controls (mean age: 39.5 ± 10.95 years) were analyzed. UPFs intake was associated with higher risk of H. pylori infection (odds ratio (OR) = 1.71; 95% confidence interval (CI): 1.05, 2.79). The association remained constant after adjustment for age, body mass index (BMI), sex, energy intake, physical activity, smoking, and alcohol status (OR = 2.17; 95% CI: 1.22, 3.86). Our data declare that UPFs consumption could have a role in increasing the likelihood of the risk of H. pylori infection. To confirm the current findings, prospective studies are suggested.
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CONTEXT: Current evidence on the effect of a low-fat (LF) diet on depression scores has been inconsistent. OBJECTIVE: To explore the effect of an LF diet on depression scores of adults by systematic review and meta-analysis of randomized controlled trials (RCTs). DATA SOURCES: The PubMed, ISI Web of Science, Scopus, and CENTRAL databases were searched from inception to June 7, 2023, to identify trials investigating the effect of an LF diet (fat intake ≤30% of energy intake) on the depression score. DATA EXTRACTION: Random-effects meta-analyses were used to estimate pooled summary effects of an LF diet on the depression score (as Hedges g). DATA ANALYSIS: Finding from 10 trials with 50â846 participants indicated no significant change in depression score following LF diets in comparison with usual diet (Hedges g = -0.11; 95% CI, -0.25 to 0.03; P = 0.12; I2 = 70.7% [for I2, 95% CI, 44%, 85%]). However, a significant improvement was observed in both usual diet and LF diets when the content of protein was 15-20% of calorie intake (LF, normal protein diet: n = 5, Hedges g = -0.21, 95% CI, -0.24 to -0.01, P = 0.04, I2 = 0%; usual, normal protein diet: n = 3, Hedges g = -0.28, 95% CI, -0.51 to -0.05, P = 0.01, I2 = 0%). Sensitivity analysis also found the depression score improved following LF diet intervention in participants without baseline depression. CONCLUSION: This study revealed that LF diet may have small beneficial effect on depression score in the studies enrolled mentally healthy participants. Moreover, achieving to adequate dietary protein is likely to be a better intervention than manipulating dietary fat to improve depression scores. However, it is not clear whether this effect will last in the long term. Conducting more studies may change the results due to the low-certainty of evidence. SYSTEMATIC REVIEW REGISTRATION: CRD42023420978 (https://www.crd.york.ac.uk/PROSPERO).
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BACKGROUND: Malnutrition is a significant concern reported in adult critically ill patients, yet there is no gold standard to assess nutritional status in this population. This study examines the association between nutritional status and clinical outcomes in intensive care unit (ICU) patients using nutritional risk assessment tools and aims to look for the best tool. METHOD: In a single-center prospective cohort study among 165 patients, the predictive performance of high or low malnutrition risk assessed by Nutritional Risk Screening (NRS), Modified Nutrition Risk in Critically Ill (m-NUTRIC), Mini-Nutritional-Assessment Short-Form (MNA-SF), Controlling Nutritional status (CONUT), and Prognostic Nutritional Index (PNI) were evaluated and compared for mortality, organ failure, length of hospitalization, and mechanical ventilation (MV). RESULTS: Different assessment tools showed various nutritional statuses. m-NUTRIC and NRS-2002 were found to be associated more strongly relative to other tools with mortality (RR = 1.72; 95% CI, 1.42-2.08) and (RR = 1.37; 95% CI, 1.08-1.72), organ failure (RR = 1.69; 95% CI, 1.44-1.96) and (RR = 1.22; 95% CI, 0.99-1.48), MV (RR = 1.46; 95% CI, 1.27-1.65) and (RR = 1.21; 95% CI, 1.04-1.39) respectively. There was no correlation between malnutrition levels assessed by mentioned tools except for NRS-2002 and length of hospitalization. In predicting mortality or illness severity, the cut points were different for some tools like NUTRIC-score and all assessed outcomes (3.5), MNA-SF and mortality (6.5), CONUT with mortality, and MV (6.5). CONCLUSIONS: A considerable proportion of patients admitted to the ICU are at high risk for malnutrition. Compared to other tools, m-NUTRIC and NRS-2002 proved superior in predicting clinical outcomes in critically ill patients. Other tools overestimated the risk of malnutrition in the ICU so couldn't predict clinical outcomes correctly.
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PURPOSE: This study conducted in Dena County is a population-based cohort study as part of the Prospective Epidemiological Research Studies in Iran (PERSIAN). The specific objectives of this study were to estimate the prevalence of region-specific modifiable risk factors and their associations with the incidence of major non-communicable diseases (NCDs). PARTICIPANTS: This PERSIAN Dena Cohort Study (PDCS) was conducted on 1561 men and 2069 women aged 35-70 years from October 2016 in Dena County, Kohgiluyeh and Boyer-Ahmad Province, Southwest Iran. The overall participation rate was 82.7%. FINDINGS TO DATE: Out of 3630 participants, the mean age was 50.16 years, 2069 (56.9%) were women and 2092 (57.6%) were rural residents. Females exhibited higher prevalence rates of diabetes, hypertension, fatty liver, psychiatric disorders, thyroiditis, kidney stones, gallstones, rheumatic disease, chronic lung disease, depression and osteoporosis compared with males (p<0.05). Furthermore, the urban population showed elevated rates of diabetes, thyroiditis, kidney stones and epilepsy, whereas psychiatric disorders and lupus were more prevalent in rural areas (p<0.05). According to laboratory findings, 418 (13.0%), 1536 (48.1%) and 626 (19.3%) of the participants had fasting blood sugar >126 mg/dL, low-density lipoprotein >100 mg/dL and haematuria, respectively; most of them were female and urban people (p<0.05). FUTURE PLANS: PDCS will be planned to re-evaluate NCD-related incidence, all-cause and cause-specific mortality every 5 years, along with annual follow-up for 15 years. Some examples of additional planned studies are evaluation of genetic, environmental risk, spirometry and ECG tests.
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Diabetes Mellitus , Cálculos Renales , Enfermedades no Transmisibles , Tiroiditis , Masculino , Humanos , Femenino , Persona de Mediana Edad , Estudios de Cohortes , Enfermedades no Transmisibles/epidemiología , Estudios Prospectivos , Irán/epidemiología , Factores de Riesgo , Diabetes Mellitus/epidemiología , PrevalenciaRESUMEN
Tea is one of the most commonly consumed beverages in the world. Morocco, Japan, and China have consumed green tea for centuries. White tea, which is a variety of green teas, is very popular in China and is highly revered for its taste. Presently, both teas are consumed in other countries around the world, even as functional ingredients, and novel research is constantly being conducted in these areas. We provide an update on the health benefits of white and green teas in this review, based on recent research done to present. After a general introduction, we focused on tea's anti-obesity and human health-promoting potential, adverse effects, and new approaches to tea and its bioactive compounds. It has been found that the health benefits of tea are due to its bioactive components, mainly phenolic compounds. Of these, catechins are the most abundant. This beverage (or its extracts) has potential anti-inflammatory and antioxidant properties, which could contribute to body weight control and the improvement of several chronic diseases. However, some studies have mentioned the possibility of toxic effects; therefore, reducing tea consumption is a good idea, especially during the last trimester of pregnancy. Additionally, new evidence will provide insight into the possible effects of tea on the human gut microbiota, and even on the viruses responsible for SARS-CoV-2. A beverage such as this may favor beneficial gut microbes, which may have important implications due to the influence of gut microbiota on human health.
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BACKGROUND: Obesity is a major risk factor for chronic diseases. Politicians and practitioners should be aware of the dramatic increase in obesity and its subsequent complications to prevent associated health risks. This systematic review aimed to provide better insight into the prevalence of overweight and obesity in the Iranian population. METHOD: An evaluation was conducted on all published observational studies from both national (SID, Irandoc, Iranmedex) and international (Web of Knowledge, PubMed, Scopus) sources, which reported the prevalence of overweight/obesity among normal population samples, between January 2012 and December 2021. RESULT: A total of 152 eligible studies were included in this meta-analysis. Of the 152 selected studies, 74 reported the prevalence of overweight/obesity in patients aged ≤ 18 years, and 61 studies in adults. In the rest of the articles (17 studies), the results were reported for a combination of these age groups. The prevalence of overweight and obesity in Iran was estimated at 20.1 (95% CI 17.92-22.30) and 13.44 (95% CI 11.76-15.22), respectively. This percentage (95% CI) was 11.71 (10.98-12.46) for overweight and 8.08 (7.02-9.22) for obesity in those aged ≤ 18 years, and 35.26 (32.61-37.99) for overweight and 21.38 (19.61-23.20) for obesity in those aged > 18 years. The overall prevalence of overweight and obesity in the entire population was 35.09% (95% CI 31.31-38.98). CONCLUSION: As obesity is on the rise in Iran, we should seek both weight loss strategies and ways to control comorbidities associated with high BMI.
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Obesidad , Sobrepeso , Adulto , Humanos , Irán , Prevalencia , Factores de RiesgoRESUMEN
Coronavirus disease 2019 (COVID-19), a novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is now at pandemic levels leading to considerable morbidity and mortality throughout the globe. Patients with obesity, diabetes, and metabolic syndrome (MetS) are mainly susceptible and more probably to get severe side effects when affected by this virus. The pathophysiologic mechanisms for these notions have not been completely known. The pro-inflammatory milieu observed in patients with metabolic disruption could lead to COVID-19-mediated host immune dysregulation, such as immune dysfunction, severe inflammation, microvascular dysfunction, and thrombosis. The present review expresses the current knowledge regarding the influence of obesity, diabetes mellitus, and MetS on COVID-19 infection and severity, and their pathophysiological mechanisms.
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Starch phosphorylation by starch-related dikinases glucan, water dikinase (GWD) and phosphoglucan, water dikinase (PWD) is a key step in starch degradation. Little information is known about the precise structure of the glucan substrate utilized by the dikinases and about the mechanisms by which these structures may be influenced. A 50-kDa starch-binding protein named EARLY STARVATION1 (ESV1) was analyzed regarding its impact on starch phosphorylation. In various in vitro assays, the influences of the recombinant protein ESV1 on the actions of GWD and PWD on the surfaces of native starch granules were analyzed. In addition, we included starches from various sources as well as truncated forms of GWD. ESV1 preferentially binds to highly ordered, α-glucans, such as starch and crystalline maltodextrins. Furthermore, ESV1 specifically influences the action of GWD and PWD at the starch granule surface. Starch phosphorylation by GWD is decreased in the presence of ESV1, whereas the action of PWD increases in the presence of ESV1. The unique alterations observed in starch phosphorylation by the two dikinases are discussed in regard to altered glucan structures at the starch granule surface.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Fosfotransferasas (Aceptores Pareados)/metabolismo , Almidón/metabolismo , Arabidopsis/enzimología , Clonación Molecular , FosforilaciónRESUMEN
The binding of photosystem I (PS I) from Thermosynechococcus elongatus to the native cytochrome (cyt) c6 and cyt c from horse heart (cyt cHH) was analyzed by oxygen consumption measurements, isothermal titration calorimetry (ITC), and rigid body docking combined with electrostatic computations of binding energies. Although PS I has a higher affinity for cyt cHH than for cyt c6, the influence of ionic strength and pH on binding is different in the two cases. ITC and theoretical computations revealed the existence of unspecific binding sites for cyt cHH besides one specific binding site close to P700 Binding to PS I was found to be the same for reduced and oxidized cyt cHH Based on this information, suitable conditions for cocrystallization of cyt cHH with PS I were found, resulting in crystals with a PS I:cyt cHH ratio of 1:1. A crystal structure at 3.4-Å resolution was obtained, but cyt cHH cannot be identified in the electron density map because of unspecific binding sites and/or high flexibility at the specific binding site. Modeling the binding of cyt c6 to PS I revealed a specific binding site where the distance and orientation of cyt c6 relative to P700 are comparable with cyt c2 from purple bacteria relative to P870 This work provides new insights into the binding modes of different cytochromes to PS I, thus facilitating steps toward solving the PS I-cyt c costructure and a more detailed understanding of natural electron transport processes.
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Proteínas Bacterianas/metabolismo , Cianobacterias/metabolismo , Citocromos c6/metabolismo , Citocromos c/metabolismo , Complejo de Proteína del Fotosistema I/metabolismo , Animales , Proteínas Bacterianas/química , Sitios de Unión , Cianobacterias/química , Citocromos c/química , Citocromos c6/química , Caballos , Simulación del Acoplamiento Molecular , Concentración Osmolar , Complejo de Proteína del Fotosistema I/química , Electricidad EstáticaRESUMEN
Artificial light-driven signal chains are particularly important for the development of systems converting light into a current, into chemicals or for light-induced sensing. Here, we report on the construction of an all-protein, light-triggered, catalytic circuit based on photosystem I, cytochrome c (cyt c) and human sulfite oxidase (hSOX). The defined assembly of all components using a modular design results in an artificial biohybrid electrode architecture, combining the photophysical features of PSI with the biocatalytic properties of hSOX for advanced light-controlled bioelectronics. The working principle is based on a competitive switch between electron supply from the electrode or by enzymatic substrate conversion.
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Biotecnología , Citocromos c/metabolismo , Técnicas Electroquímicas , Complejo de Proteína del Fotosistema I/metabolismo , Sulfito-Oxidasa/metabolismo , Biocatálisis , Citocromos c/química , Electrodos , Humanos , Luz , Complejo de Proteína del Fotosistema I/química , Sulfito-Oxidasa/químicaRESUMEN
The structure of monomeric and trimeric photosystem I (PS I) of Thermosynechococcus elongatus BP1 (T. elongatus) was investigated by small-angle X-ray scattering (SAXS). The scattering data reveal that the protein-detergent complexes possess radii of gyration of 58 and 78 Å in the cases of monomeric and trimeric PS I, respectively. The results also show that the samples are monodisperse, virtually free of aggregation, and contain empty detergent micelles. The shape of the protein-detergent complexes can be well approximated by elliptical cylinders with a height of 78 Å. Monomeric PS I in buffer solution exhibits minor and major radii of the elliptical cylinder of about 50 and 85 Å, respectively. In the case of trimeric PS I, both radii are equal to about 110 Å. The latter model can be shown to accommodate three elliptical cylinders equal to those describing monomeric PS I. A structure reconstitution also reveals that the protein-detergent complexes are larger than their respective crystal structures. The reconstituted structures are larger by about 20 Å mainly in the region of the hydrophobic surfaces of the monomeric and trimeric PS I complexes. This seeming contradiction can be resolved by the addition of a detergent belt constituted by a monolayer of dodecyl-ß-D-maltoside molecules. Assuming a closest possible packing, a number of roughly 1024 and 1472 detergent molecules can be determined for monomeric and trimeric PS I, respectively. Taking the monolayer of detergent molecules into account, the solution structure can be almost perfectly modeled by the crystal structures of monomeric and trimeric PS I.
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Proteínas Bacterianas/química , Complejo de Proteína del Fotosistema I/química , Multimerización de Proteína , Dispersión del Ángulo Pequeño , Synechococcus/metabolismo , Difracción de Rayos X , Detergentes/química , Modelos Moleculares , Complejo de Proteína del Fotosistema I/metabolismo , Soluciones , Espectrometría de Masa por Láser de Matriz Asistida de Ionización DesorciónRESUMEN
The engineering of renewable and sustainable protein-based light-to-energy converting systems is an emerging field of research. Here, we report on the development of supramolecular light-harvesting electrodes, consisting of the redox protein cytochrome c working as a molecular scaffold as well as a conductive wiring network and photosystem I as a photo-functional matrix element. Both proteins form complexes in solution, which in turn can be adsorbed on thiol-modified gold electrodes through a self-assembly mechanism. To overcome the limited stability of self-grown assemblies, DNA, a natural polyelectrolyte, is used as a further building block for the construction of a photo-active 3D architecture. DNA acts as a structural matrix element holding larger protein amounts and thus remarkably improving the maximum photocurrent and electrode stability. On investigating the photophysical properties, this system demonstrates that effective electron pathways have been created.
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Citocromos c/química , ADN/química , Complejo de Proteína del Fotosistema I/química , Ingeniería de Proteínas , Cianobacterias/enzimología , Electrodos , Oxidación-ReducciónRESUMEN
One major vital element of the oxygenic photosynthesis is photosystem I (PSI). We report on the construction of graphene-based nanohybrid light-harvesting architectures consisting of PSI supercomplexes adsorbed onto π-system-modified graphene interfaces. The light-driven nanophotobioelectrochemical architectures have been designed on a modified carbon surface, on the basis of π-π-stacking interactions between polycyclic aromatic compounds and graphene. As a result of the remarkable features of graphene and the feasibility of purposeful surface property adjustment, well-defined photoelectrochemical responses have been displayed by the nanophotohybrid electrodes. In particular, the PSI-graphene electrodes utilizing naphthalene derivatives provided a suitable surface for the adsorption of PSI and display already at the open circuit potential (OCP) a high cathodic photocurrent output of 4.5 ± 0.1 µA/cm(2). By applying an overpotential and addition of a soluble electron acceptor (methyl viologen), the photocurrent density can be further magnified to 20 ± 0.5 µA/cm(2). On the contrary, the investigated anthracene-based PSI-graphene electrodes exhibit considerably smaller and not very directed photoelectrochemical responses. This study grants insights into the influences of different polycyclic aromatic compounds acting as an interface between the very large protein supercomplex PSI and graphene while supporting the electrochemical communication of the biomolecule with the electrode. It needs to be emphasized that solely the naphthalene-based photoelectrodes reveal unidirectional cathodic photocurrents, establishing the feasibility of utilizing this advanced approach for the construction of next-generation photovoltaic devices.
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Electroquímica , Grafito/metabolismo , Nanoestructuras/química , Fotoquímica , Complejo de Proteína del Fotosistema I/metabolismo , Adsorción , Electrodos , Grafito/química , Estructura Molecular , Complejo de Proteína del Fotosistema I/química , Propiedades de SuperficieRESUMEN
Glucan, water dikinase (GWD) is a key enzyme of starch metabolism but the physico-chemical properties of starches isolated from GWD-deficient plants and their implications for starch metabolism have so far not been described. Transgenic Arabidopsis thaliana plants with reduced or no GWD activity were used to investigate the properties of starch granules. In addition, using various in vitro assays, the action of recombinant GWD, ß-amylase, isoamylase and starch synthase 1 on the surface of native starch granules was analysed. The internal structure of granules isolated from GWD mutant plants is unaffected, as thermal stability, allomorph, chain length distribution and density of starch granules were similar to wild-type. However, short glucan chain residues located at the granule surface dominate in starches of transgenic plants and impede GWD activity. A similarly reduced rate of phosphorylation by GWD was also observed in potato tuber starch fractions that differ in the proportion of accessible glucan chain residues at the granule surface. A model is proposed to explain the characteristic morphology of starch granules observed in GWD transgenic plants. The model postulates that the occupancy rate of single glucan chains at the granule surface limits accessibility to starch-related enzymes.
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Proteínas de Arabidopsis/metabolismo , Fosfotransferasas (Aceptores Pareados)/metabolismo , Almidón/química , Almidón/metabolismo , Proteínas de Arabidopsis/genética , Glucosiltransferasas/genética , Glucosiltransferasas/metabolismo , Isoamilasa/metabolismo , Proteínas de Transporte de Monosacáridos/genética , Proteínas de Transporte de Monosacáridos/metabolismo , Mutación , Fosforilación , Fosfotransferasas (Aceptores Pareados)/genética , Plantas Modificadas Genéticamente , Solanum tuberosum , Almidón/genética , Almidón/ultraestructura , Propiedades de Superficie , beta-Amilasa/metabolismoRESUMEN
Starch phosphorylation mediated by the α-glucan, water dikinase (GWD) is crucial for transitory starch metabolism. The impact of the GWD action on transitory starch metabolism was analyzed in Arabidopsis mutants either lacking or revealing different reduced levels of GWD activity. In these mutants, glucose 6-phosphate (G6P) levels of the transitory leaf starch, the average leaf starch content, as well as alterations in the growth phenotype were determined under different light length conditions, including continuous light. Based on biochemical and growth phenotypical data, we found that the length of the light phase affects the phosphorylation state of the transitory starch and, by this, the average leaf starch content and the resulting growth of the plants. Additionally, we discuss data referring to an involvement of the GWD mediated glucan phosphorylation in starch synthesis, as, e.g., starch phosphorylation occurred even when a dark phase was omitted.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Glucanos/metabolismo , Luz , Fosfotransferasas (Aceptores Pareados)/metabolismo , Fotoperiodo , Hojas de la Planta/metabolismo , Almidón/metabolismo , Arabidopsis/crecimiento & desarrollo , Glucosa-6-Fosfato/metabolismo , Fosforilación , Plastidios/metabolismo , AguaRESUMEN
Many plants accumulate substantial starch reserves in their leaves during the day and remobilize them at night to provide carbon and energy for maintenance and growth. In this paper, we explore the role of a sugar-signaling metabolite, trehalose-6-phosphate (Tre6P), in regulating the accumulation and turnover of transitory starch in Arabidopsis (Arabidopsis thaliana) leaves. Ethanol-induced overexpression of trehalose-phosphate synthase during the day increased Tre6P levels up to 11-fold. There was a transient increase in the rate of starch accumulation in the middle of the day, but this was not linked to reductive activation of ADP-glucose pyrophosphorylase. A 2- to 3-fold increase in Tre6P during the night led to significant inhibition of starch degradation. Maltose and maltotriose did not accumulate, suggesting that Tre6P affects an early step in the pathway of starch degradation in the chloroplasts. Starch granules isolated from induced plants had a higher orthophosphate content than granules from noninduced control plants, consistent either with disruption of the phosphorylation-dephosphorylation cycle that is essential for efficient starch breakdown or with inhibition of starch hydrolysis by ß-amylase. Nonaqueous fractionation of leaves showed that Tre6P is predominantly located in the cytosol, with estimated in vivo Tre6P concentrations of 4 to 7 µm in the cytosol, 0.2 to 0.5 µm in the chloroplasts, and 0.05 µm in the vacuole. It is proposed that Tre6P is a component in a signaling pathway that mediates the feedback regulation of starch breakdown by sucrose, potentially linking starch turnover to demand for sucrose by growing sink organs at night.
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Arabidopsis/metabolismo , Retroalimentación Fisiológica/fisiología , Hojas de la Planta/metabolismo , Almidón/metabolismo , Fosfatos de Azúcar/metabolismo , Trehalosa/análogos & derivados , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cloroplastos/metabolismo , Gránulos Citoplasmáticos/metabolismo , Gránulos Citoplasmáticos/ultraestructura , Citosol/metabolismo , Etanol/farmacología , Glucosiltransferasas/metabolismo , Hidrólisis/efectos de los fármacos , Immunoblotting , Maltosa/metabolismo , Microscopía Electrónica de Rastreo , Fosfatos/metabolismo , Hojas de la Planta/efectos de los fármacos , Plantas Modificadas Genéticamente , Almidón/ultraestructura , Factores de Tiempo , Trehalosa/metabolismo , Trisacáridos/metabolismoRESUMEN
The plant genome encodes at least two distinct and evolutionary conserved plastidial starch-related dikinases that phosphorylate a low percentage of glucosyl residues at the starch granule surface. Esterification of starch favours the transition of highly ordered α-glucans to a less ordered state and thereby facilitates the cleavage of interglucose bonds by hydrolases. Metabolically most important is the phosphorylation at position C6, which is catalysed by the glucan, water dikinase (GWD). The reactions mediated by recombinant wild-type GWD from Arabidopsis thaliana (AtGWD) and from Solanum tuberosum (StGWD) were studied. Two mutated proteins lacking the conserved histidine residue that is indispensible for glucan phosphorylation were also included. The wild-type GWDs consume approximately 20% more ATP than is required for glucan phosphorylation. Similarly, although incapable of phosphorylating α-glucans, the two mutated dikinase proteins are capable of degrading ATP. Thus, consumption of ATP and phosphorylation of α-glucans are not strictly coupled processes but, to some extent, occur as independent phosphotransfer reactions. As revealed by incubation of the GWDs with [γ-(33) P]ATP, the consumption of ATP includes the transfer of the γ-phosphate group to the GWD protein but this autophosphorylation does not require the conserved histidine residue. Thus, the GWD proteins possess two vicinal phosphorylation sites, both of which are transiently phosphorylated. Following autophosphorylation at both sites, native dikinases flexibly use various terminal phosphate acceptors, such as water, α-glucans, AMP and ADP. A model is presented describing the complex phosphotransfer reactions of GWDs as affected by the availability of the various acceptors.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimología , Glucanos/metabolismo , Fosfotransferasas (Aceptores Pareados)/metabolismo , Plastidios/enzimología , Solanum tuberosum/enzimología , Adenosina Difosfato/metabolismo , Adenosina Monofosfato/metabolismo , Adenosina Trifosfato/metabolismo , Proteínas de Arabidopsis/genética , Biocatálisis , Histidina/metabolismo , Cinética , Fosforilación , Fosfotransferasas (Aceptores Pareados)/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Agua/metabolismoRESUMEN
Almost all glucosyl transfer reactions rely on glucose-1-phosphate (Glc-1-P) that either immediately acts as glucosyl donor or as substrate for the synthesis of the more widely used Glc dinucleotides, ADPglucose or UDPglucose. In this communication, we have analyzed two Glc-1-P-related processes: the carbon flux from externally supplied Glc-1-P to starch by either mesophyll protoplasts or intact chloroplasts from Arabidopsis (Arabidopsis thaliana). When intact protoplasts or chloroplasts are incubated with [U-(14)C]Glc-1-P, starch is rapidly labeled. Incorporation into starch is unaffected by the addition of unlabeled Glc-6-P or Glc, indicating a selective flux from Glc-1-P to starch. However, illuminated protoplasts incorporate less (14)C into starch when unlabeled bicarbonate is supplied in addition to the (14)C-labeled Glc-1-P. Mesophyll protoplasts incubated with [U-(14)C]Glc-1-P incorporate (14)C into the plastidial pool of adenosine diphosphoglucose. Protoplasts prepared from leaves of mutants of Arabidopsis that lack either the plastidial phosphorylase or the phosphoglucomutase isozyme incorporate (14)C derived from external Glc-1-P into starch, but incorporation into starch is insignificant when protoplasts from a mutant possessing a highly reduced ADPglucose pyrophosphorylase activity are studied. Thus, the path of assimilatory starch biosynthesis initiated by extraplastidial Glc-1-P leads to the plastidial pool of adenosine diphosphoglucose, and at this intermediate it is fused with the Calvin cycle-driven route. Mutants lacking the plastidial phosphoglucomutase contain a small yet significant amount of transitory starch.
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Arabidopsis/metabolismo , Cloroplastos/metabolismo , Glucofosfatos/metabolismo , Hojas de la Planta/metabolismo , Protoplastos/metabolismo , Arabidopsis/enzimología , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Transporte Biológico , Isótopos de Carbono/análisis , Cloroplastos/enzimología , Glucosa-1-Fosfato Adenililtransferasa/metabolismo , Glucosiltransferasas/genética , Glucosiltransferasas/metabolismo , Mutación , Almidón/biosíntesisRESUMEN
Reserve starch is an important plant product but the actual biosynthetic process is not yet fully understood. Potato (Solanum tuberosum) tuber discs from various transgenic plants were used to analyse the conversion of external sugars or sugar derivatives to starch. By using in vitro assays, a direct glucosyl transfer from glucose 1-phosphate to native starch granules as mediated by recombinant plastidial phosphorylase was analysed. Compared with labelled glucose, glucose 6-phosphate or sucrose, tuber discs converted externally supplied [(14)C]glucose 1-phosphate into starch at a much higher rate. Likewise, tuber discs from transgenic lines with a strongly reduced expression of cytosolic phosphoglucomutase, phosphorylase or transglucosidase converted glucose 1-phosphate to starch with the same or even an increased rate compared with the wild-type. Similar results were obtained with transgenic potato lines possessing a strongly reduced activity of both the cytosolic and the plastidial phosphoglucomutase. Starch labelling was, however, significantly diminished in transgenic lines, with a reduced concentration of the plastidial phosphorylase isozymes. Two distinct paths of reserve starch biosynthesis are proposed that explain, at a biochemical level, the phenotype of several transgenic plant lines.