Methionine synthesis from 3-methylthioribose in apple tissue

The primary fate of 5-methylthioribose in apple tissue is the formation of methionine. Using dual labeled 5-methylthioribose, it was shown that both the CH₃S- group and the ribose portion of 5-methylthioribose were equally incorporated into methionine. Thus, the pathway involves modification of the ribose portion of 5-methylthioribose into the 2-aminobutyrate portion of methionine. This pathway functions to recycle methionine for continued synthesis of ethylene in fruit tissues. The methionine cycle in relation to ethylene biosynthesis is presented.     

Studies on uridine diphosphate-galactose pyrophosphatase and uridine diphosphate-galactose: glycoprotein galactosyltransferase activities in microsomal membranes.

Rat liver microsomes showed very active uridine diphosphate-galactose pyrophosphatase activity leading to the hydrolysis of uridine diphosphate-galactose into galactose1-phosphate and finally into galactose. The activity was observed in presence of buffers with wide ranges of pH. Different concentrations of divalent cations, such as Mn²⁺, Mg²⁺, and Ca²⁺ had no significant effect on the enzyme activity. A number of nucleotides and their derivatives inhibited the pyrophosphatase activity. Of these, different concentrations of uridine monophosphate, cytidine 5′-phosphate and cytidine 5′-diphosphate have slight or no effect; cytidine 5′-triphosphate, adenosine 5′-triphosphate, guanosine 5′-triphosphate, cytidine 5′-diphosphate-glucose and guanosine 5′-diphosphate-glucose showed strong inhibitory effect whereas cytidine 5′-diphosphate-choline showed a moderate effect on the pyrophosphatase. All these nucleotides also showed variable stimulatory effects on uridine diphosphate-galactose:glycoprotein galactosyltransferase activity in the microsomes which could be partly related to their inhibitory effects on uridine diphosphate-galactose pyrophosphatase. Among them uridine monophosphate, cytidine 5′-phosphate, and cytidine 5′-diphosphate stimulated galactosyltransferase activity without showing appreciable inhibition of pyrophosphatase, cytidine 5′-diphosphate-choline, although did not inhibit pyrophosphatase as effectively as cytidine 5′-triphosphate, guanosine 5′-triphosphate, adenosine 5′-triphosphate, cytidine 5′-diphosphate-glucose, and guanosine 5′-diphosphate-glucose but stimulated galactosyltransferase activity as well as those. The fact that cytidine 5′-diphosphate-choline stimulated galactosyltransferase more effectively than cytidine 5′-phosphate, cytidine 5′-diphosphate, and cytidine 5′-triphosphate suggested an additional role of the choline moiety in the system. It has been also shown that cytidine 5′-diphosphate-choline can affect the saturation of galactosyltransferase enzyme at a much lower concentration of uridine diphosphate-galactose. Most of the pyrophosphatase and galactosyltransferase activities were solubilized by deoxycholate and the membrane pellets remaining after solubilization still retained some galactosyltransferase activity which was stimulated by cytidine 5′-diphosphate-choline. In different membrane fractions a concerted effect of both uridine diphosphate-galactose pyrophosphatase and glycoprotein:galactosyltransferase enzymes on the substrate uridine diphosphate-galactose is indicated and their eventual controlling effects on the glycopolymer synthesis in vitro or in vivo need careful evaluation.     

Formation of collagen-glycosaminoglycan blended nanofibrous scaffolds and their biological properties

The development of blended collagen and glycosaminoglycan (GAG) scaffolds can potentially be used in many soft tissue engineering applications since the scaffolds mimic the structure and biological function of native extracellular matrix (ECM). In this study, we were able to obtain novel nanofibrous collagen-GAG scaffolds by electrospinning collagen blended with chondroitin sulfate (CS), a widely used GAG, in a mixed solvent of trifluoroethanol and water. The electrospun collagen-GAG scaffold with 4% CS (COLL-CS-04) exhibited a uniform fiber structure with nanoscale diameters. A second collagen-GAG scaffold with 10% CS consisted of smaller diameter fibers but exhibited a broader diameter distribution due to the different solution properties in comparison with COLL-CS-04. After cross-linking with glutaraldehyde vapor, the collagen-GAG scaffolds became more biostable and were resistant to collagenase degradation. This is evidently a more favorable environment allowing increased proliferation of rabbit conjunctiva fibroblast on the scaffolds. Incorporation of CS into collagen nanofibers without cross-linking did not increase the biostability but still promoted cell growth. The potential of applying the nanoscale collagen-GAG scaffold in tissue engineering is significant since the nanodimension fibers made of natural ECM mimic closely the native ECM found in the human body. The high surface area characteristic of this scaffold may maximize cell-ECM interaction and promote tissue regeneration faster than other conventional scaffolds.     

Fasting up‐regulates ferroportin 1 expression via a Ghrelin/GHSR/MAPK signaling pathway

The significant positive correlation between ghrelin and iron and hepcidin levels in the plasma of children with iron deficiency anemia prompted us to hypothesize that ghrelin may affect iron metabolism. Here, we investigated the effects of fasting or ghrelin on the expression of hepcidin, ferroportin 1 (Fpn1), transferrin receptor 1 (TfR1), ferritin light chain (Ft‐L) proteins, and ghrelin, and also hormone secretagogue receptor 1 alpha (GHSR1α) and ghrelin O‐acyltransferase (GOAT) mRNAs in the spleen and/or macrophage. We demonstrated that fasting induces a significant increase in the expression of ghrelin, GHSR1α, GOAT, and hepcidin mRNAs, as well as Ft‐L and Fpn1 but not TfR1 proteins in the spleens of mice in vivo. Similar to the effects of fasting on the spleen, ghrelin induced a significant increase in the expression of Ft‐L and Fpn1 but not TfR1 proteins in macrophages in vitro. In addition, ghrelin was found to induce a significant enhancement in phosphorylation of ERK as well as translocation of pERK from the cytosol to nuclei. Furthermore, the increased pERK and Fpn1 induced by ghrelin was demonstrated to be preventable by pre‐treatment with either GHSR1α antagonist or pERK inhibitor. Our findings support the hypothesis that fasting upregulates Fpn1 expression, probably via a ghrelin/GHSR/MAPK signaling pathway.     

Periplasmic localization of nicotinate phosphoribosyltransferase in Escherichia coli.

Nicotinate phosphoribosyltransferase (NAPRTase) in Escherichia coli mediates the formation of nicotinate mononucleotide, a direct precursor of nicotinamide adenine dinucleotide (NAD), from nicotinate and 5-phosphoribosyl-1-pyrophosphate. Specifically, NAPRTase contributes to NAD synthesis by utilizing intracellular nicotinate formed from NAD degradation products, which are recycled by NAD cycle enzymes and exogenous nicotinate when it is available. In previous studies, it has been tacitly assumed that almost all NAD cycle enzymes are localized in the cytoplasm of E. coli. The results of this investigation provide evidence that NAPRTase is a periplasmic (extracytoplasmic) enzyme. The osmotic shock of exponential-phase cells of E. coli K-12 and ML 308-225 resulted in the release of 63 to 72% and 42 to 48%, respectively, of the NAPRTase into the shock medium. In addition, when exponential cells of strains K-12 and ML 308-225 were converted into spheroplasts, 75 to 84% and 54 to 68%, respectively, of the enzyme was released into the spheroplast medium. Since previous estimates of the effective levels of NAPRTase present in putative repressed and derepressed E. coli cells appeared to be very low, a more convenient and accurate alternative method for the evaluation of NAPRTase in whole cells was developed. The results show that NAPRTase is subject only to a modest degree of enzyme repression. In addition, no evidence was found for the presence of a protein or low-molecular-weight inhibitor of the enzyme in repressed cells.     

New Class of Ni‐Rich Cathode Materials Li[NixCoyB1−x−y]O2 for Next Lithium Batteries

A new class of layered cathodes, Li[Ni_xCo_yB_1?x?y]O₂ (NCB), is synthesized. The proposed NCB cathodes have a unique microstructure in which elongated primary particles are tightly packed into spherical secondary particles. The cathodes also exhibit a strong crystallographic texture in which the a–b layer planes are aligned along the radial direction, facilitating Li migration. The microstructure, which effectively suppresses the formation of microcracks, improves the cycling stability of the NCB cathodes. The NCB cathode with 1.5 mol% B delivers a discharge capacity of 234 mAh g^?1 at 0.1 C and retains 91.2% of its initial capacity after 100 cycles (compared to values of 229 mAh g^?1 at 0.1 C and 78.8% for pristine Li[Ni_0.9Co_0.1]O₂). This study shows the importance of controlling the microstructure to obtain the required cycling stability, especially for Ni‐rich layered cathodes, where the main cause of capacity fading is related to mechanical strain in their charged state.     

GeSUT4 mediates sucrose import at the symbiotic interface for carbon allocation of heterotrophic Gastrodia elata (Orchidaceae)

Gastrodia elata, a fully mycoheterotrophic orchid without photosynthetic ability, only grows symbiotically with the fungus Armillaria. The mechanism of carbon distribution in this mycoheterotrophy is unknown. We detected high sucrose concentrations in all stages of Gastrodia tubers, suggesting sucrose may be the major sugar transported between fungus and orchid. Thick symplasm‐isolated wall interfaces in colonized and adjacent large cells implied involvement of sucrose importers. Two sucrose transporter (SUT)‐like genes, GeSUT4 and GeSUT3, were identified that were highly expressed in young Armillaria‐colonized tubers. Yeast complementation and isotope tracer experiments confirmed that GeSUT4 functioned as a high‐affinity sucrose‐specific proton‐dependent importer. Plasma‐membrane/tonoplast localization of GeSUT4‐GFP fusions and high RNA expression of GeSUT4 in symbiotic and large cells indicated that GeSUT4 likely functions in active sucrose transport for intercellular allocation and intracellular homeostasis. Transgenic Arabidopsis overexpressing GeSUT4 had larger leaves but were sensitive to excess sucrose and roots were colonized with fewer mutualistic Bacillus, supporting the role of GeSUT4 in regulating sugar allocation. This is not only the first documented carbon import system in a mycoheterotrophic interaction but also highlights the evolutionary importance of sucrose transporters for regulation of carbon flow in all types of plant‐microbe interactions.