Insights into the binding behavior of native and non-native cytochromes to photosystem I from Thermosynechococcus elongatus.

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.

EARLY STARVATION1 specifically affects the phosphorylation action of starch-related dikinases.

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.

Bioelectronic Circuit on a 3D Electrode Architecture: Enzymatic Catalysis Interconnected with Photosystem I.

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.

Solution structure of monomeric and trimeric photosystem I of Thermosynechococcus elongatus investigated by small-angle X-ray scattering.

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.

Unidirectional Photocurrent of Photosystem I on π-System-Modified Graphene Electrodes: Nanobionic Approaches for the Construction of Photobiohybrid Systems.

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.

Phosphorylation of transitory starch by α-glucan, water dikinase during starch turnover affects the surface properties and morphology of starch granules.

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.

Feedback inhibition of starch degradation in Arabidopsis leaves mediated by trehalose 6-phosphate.

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.

Effect of Low-Fat Diet on Depression Score in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Clinical Trials.

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 50 846 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).

Relation between nutritional status on clinical outcomes of critically ill patients: emphasizing nutritional screening tools in a prospective cohort investigation.

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.

Cohort profile: the PERSIAN Dena Cohort Study (PDCS) of non-communicable diseases in Southwest Iran.

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.

Tea's anti-obesity properties, cardiometabolic health-promoting potentials, bioactive compounds, and adverse effects: A review focusing on white and green teas.

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.

Prevalence of overweight and obesity among Iranian population: a systematic review and meta-analysis.

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.

Glucose-1-phosphate transport into protoplasts and chloroplasts from leaves of Arabidopsis.

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.

Obesity, Diabetes Mellitus, and Metabolic Syndrome: Review in the Era of COVID-19.

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.

The Laforin-like dual-specificity phosphatase SEX4 from Arabidopsis hydrolyzes both C6- and C3-phosphate esters introduced by starch-related dikinases and thereby affects phase transition of alpha-glucans.

The biochemical function of the Laforin-like dual-specific phosphatase AtSEX4 (EC 3.1.3.48) has been studied. Crystalline maltodextrins representing the A- or the B-type allomorph were prephosphorylated using recombinant glucan, water dikinase (StGWD) or the successive action of both plastidial dikinases (StGWD and AtPWD). AtSEX4 hydrolyzed carbon 6-phosphate esters from both the prephosphorylated A- and B-type allomorphs and the kinetic constants are similar. The phosphatase also acted on prelabeled carbon-3 esters from both crystalline maltodextrins. Similarly, native starch granules prelabeled in either the carbon-6 or carbon-3 position were also dephosphorylated by AtSEX4. The phosphatase did also hydrolyze phosphate esters of both prephosphorylated maltodextrins when the (phospho)glucans had been solubilized by heat treatment. Submillimolar concentrations of nonphosphorylated maltodextrins inhibited AtSEX4 provided they possessed a minimum of length and had been solubilized. As opposed to the soluble phosphomaltodextrins, the AtSEX4-mediated dephosphorylation of the insoluble substrates was incomplete and at least 50% of the phosphate esters were retained in the pelletable (phospho)glucans. The partial dephosphorylation of the insoluble glucans also strongly reduced the release of nonphosphorylated chains into solution. Presumably, this effect reflects fast structural changes that following dephosphorylation occur near the surface of the maltodextrin particles. A model is proposed defining distinct stages within the phosphorylation/dephosphorylation-dependent transition of alpha-glucans from the insoluble to the soluble state.

Glucose 1-phosphate is efficiently taken up by potato (Solanum tuberosum) tuber parenchyma cells and converted to reserve starch granules.

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.

Glucan, water dikinase phosphorylates crystalline maltodextrins and thereby initiates solubilization.

Starch phosphorylation by glucan, water dikinase (GWD; EC 2.7.9.4) is an essential step in the breakdown of native starch particles, but the underlying mechanisms have remained obscure. In this paper, the initial reactions of starch degradation were analyzed using crystallized maltodextrins as model carbohydrates. As revealed by X-ray diffraction analysis, the crystallized maltodextrins represent the B-type starch allomorph. Recombinant GWD phosphorylated crystalline maltodextrins with a high specific activity (55-60 nmol mg-1 protein min-1), but exhibited very little activity with the same maltodextrins that had been solubilized by heat treatment. Recombinant phosphoglucan, water dikinase (PWD; EC 2.7.9.5) utilized the crystalline maltodextrins only when pre-phosphorylated by GWD. Phosphorylation of crystalline maltodextrins, as catalyzed by GWD, initiated solubilization of neutral as well as phosphorylated glucans. In both the insoluble and the soluble state, mono-, di- and triphosphorylated alpha-glucans were observed, with wide and overlapping ranges of degree of polymerization. Thus, the substrate specificity of the GWD is defined by the physical arrangement of alpha-glucans rather than by structural parameters, such as the distribution of branching points or degree of polymerization. Unlike GWD and PWD, recombinant beta-amylase isozyme 3 (BAM3), which has been shown to be essential for plastidial starch degradation, preferentially degraded soluble maltodextrins rather than crystallized glucans. In summary, two conclusions were reached. Firstly, carbohydrate targets of GWD are primarily defined by the molecular order of glucan helices. Secondly, GWD-catalyzed phosphorylation mediates the phase transition of glucans from a highly ordered to a less ordered and hydrated state.

Eukaryotic starch degradation: integration of plastidial and cytosolic pathways.

Starch is an important plant product widely used as a nutrient, as a source of renewable energy, and for many technological applications. In plants, starch is the almost ubiquitous storage carbohydrate whereas most heterotrophic prokaryotes and eukaryotes rely on glycogen. Despite close similarities in basic chemical features, starch and glycogen differ in both structural and physicochemical properties. Glycogen is a hydrosoluble macromolecule with evenly distributed branching points. Starch exists as a water-insoluble particle having a defined (and evolutionary conserved) internal structure. The biochemistry of starch requires the co-operation of up to 40 distinct (iso)enzymes whilst approximately 10 (iso)enzymes permit glycogen metabolism. The biosynthesis and degradation of native starch include the transition of carbohydrates from the soluble to the solid phase and vice versa. In this review, two novel aspects of the eukaryotic plastidial starch degradation are discussed: Firstly, biochemical reactions that take place at the surface of particulate glucans and mediate the phase transition of carbohydrates. Secondly, processes that occur downstream of the export of starch-derived sugars into the cytosol. Degradation of transitory starch mainly results in the formation of neutral sugars, such as glucose and maltose, that are transported into the cytosol via the respective translocators. The cytosolic metabolism of the neutral sugars includes the action of a hexokinase, a phosphoglucomutase, and a transglucosidase that utilizes high molecular weight glycans as a transient glucosyl acceptor or donor. Data are included on the transglucosidase (disproportionating isozyme 2) in Cyanophora paradoxa that accumulates storage carbohydrates in the cytosol rather than in the plastid.

Mass spectrometric quantification of the relative amounts of C6 and C3 position phosphorylated glucosyl residues in starch.

The quantification of phosphate bound to the C6 and C3 positions of glucose residues in starch has received increasing interest since the importance of starch phosphorylation for plant metabolism was discovered. The method described here is based on the observation that the isobaric compounds glucose-6-phosphate (Glc6P) and glucose-3-phosphate (Glc3P) exhibit significantly different fragmentation patterns in negative ion electrospray tandem mass spectrometry (MS/MS). A simple experiment involving collision-induced dissociation (CID) MS(2) spectra of the sample and the two reference substances Glc3P and Glc6P permitted the quantification of the relative amounts of the two compounds in monosaccharide mixtures generated by acid hydrolysis of starch. The method was tested on well-characterized potato tuber starch. The results are consistent with those obtained by NMR analysis. In contrast to NMR, however, the presented method is fast and can be performed on less than 1 mg of starch. Starch samples of other origins exhibiting a variety of phosphorylation degrees were analyzed to assess the sensitivity and robustness of the method.

Engineering of supramolecular photoactive protein architectures: the defined co-assembly of photosystem I and cytochrome c using a nanoscaled DNA-matrix.

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.