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Esterolytic Properties of Leucine-Proteinase, the Leucine-Specific Serine Proteinase from Spinach (Spinacia oleracea L.) Leaves : A Steady-State and Pre-Steady-State Study
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Fotosintesi
No full textLa vita sulla Terra è strettamente legata e dipendente dall’energia del Sole.
Il nostro pianeta è immerso nella luce e gli organismi che l’hanno abitato in passato e attualmente lo abitano
hanno evoluto molteplici interazioni con la luce solare.Tra queste, la Fotosintesi, e cioè la capacità di catturare e usare l’energia del Sole, rappresenta certamente il processo biologico fondamentale e unico dal quale
dipendono tutti gli organismi vivent
Esterolytic properties of leucine-proteinase, the leucine-specific serine proteinase from spinach (Spinacia oleracea L.)
No full textSteady-state and pre-steady-state kinetics for the hydrolysis of p-nitrophenyl esters of N-alpha-carbobenzoxy(-l-)amino acids catalyzed by leucine-proteinase were determined between pH 5 and 10 (I = 0.1 molar) at 23 +/- 0.5 degrees C. For the substrates considered: (a) the acylation step is rate-limiting in catalysis; (b) the pH profiles of k(cat) and k(cat)/K(m) reflect the ionization of two groups with pK(a) values ranging between 6.5 and 6.9, and 8.1 and 8.3 (probably, the histidine residue involved in the catalytic triad and the N-terminus, respectively); and (c) values of K(m) are pH independent. Among the substrates examined, N-alpha-carbobenzoxy-l-leucine-p-nitrophenyl ester shows the most favorable catalytic parameters and allows to determine an enzyme concentration as low as 5 x 10(-10) molar at the optimum pH value (approximately 7.5)
Interaction of neutral polysaccharides with phosphatidylcholine multilamellar liposomes. Phase transitions studied by the binding of fluorescein-conjugated dextrans
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Interaction of neutral polysaccharides with human erythrocyte membrane: involvement of phospholipid bilayer
No full textThe erythrocyte aggregating activity of different neutral polysacharides depends on the polymer - membrane affinity and its molecular length. Extended proteolytic and neuraminidase treatments of red blood cell membrane did not reduce aggregation induced by polysaccharides. Fluo=rescent dextran studies showed that polymer adsorption on red blood cells was measurable only for a dextran mole=cular weight above 40,000 as for cell aggregation. Identical dextran adsorption behaviour was observed for all liposomes composed of various purified phospholipids, suggesting the involvement of the phospholipid bilayer in dextran-membrane interaction. All aggregations induced by neutral polysaccha=rides were inhibited by D-and L-tryptophan. Compounds very similar to tryptophan were less active or completely inactive inhibitors. Equilibrium dialysis, gel filtration and tryptophan fluorescence studies clearly showed that there was no com=plex formation between tryptophan and neutral polysaccha=rides. Therefore tryptophan does not result an haptenic inhi=bitor, but reduces the adsorption of polysaccharides on cell membrane
A new agglutinating activity from wheat flour inhibited by tryptophan
No full textA new compound endowed with agglutinating activity, designated the flour agglutinin, was extracted from wheat flour with water and purified by gel filtration and ion-exchange chromatography. The haptenic inhibitors of the plant agglutinins do not affect flour agglutinin activity which, on the other hand, is inhibited by D- and L-tryptophan. Flour agglutinin has a molecular weight of about 5 - 10(4) as determined by gel filtration. It consists of a neutral heteropolysaccharide constituted of D-xylose and L-arabinose, and is homogeneous as judged by sedimentation analysis. Flour agglutinin activity is destroyed by treatment with Cellulase 2000 and periodate, but is not affected by alpha-amylase and proteolytic enzymes. Compared to germ agglutinin, flour agglutinin exhibits a peculiar range of cell specificity. It agglutinates several normal cell types, but has no effects on some neoplastic cells tested. Tryptic digestion of erythrocytes does not affect their susceptibility to flour agglutinin-induced agglutination
The Salt Tolerance Related Protein (STRP) Mediates Cold Stress Responses and Abscisic Acid Signalling in Arabidopsis thaliana
Full text linkLow temperature stress is one of the major causes of crop yield reduction in agriculture. The alteration of gene expression pattern and the accumulation of stress-related proteins are the main strategies activated by plants under this unfavourable condition. Here we characterize the Arabidopsis thaliana Salt Tolerance Related Protein (STRP). The protein rapidly accumulates under cold treatment, and this effect is not dependent on transcriptional activation of the STRP gene, but on the inhibition of proteasome-mediated degradation. Subcellular localization of STRP was determined by the transient expression of STRP-YFP in A. thaliana protoplasts. STRP is localized into the cytosol, nucleus, and associated to the plasma membrane. Under cold stress, the membrane-associated fraction decreases, while in the cytosol and in the nucleus STRP levels strongly increase. STRP has high similarity with WCI16, a wheat Late Embryogenesis Abundant (LEA)-like protein. Despite no canonical LEA motifs in the STRP sequence are present, physicochemical characterization demonstrated that STRP shares common features with LEA proteins, being a high hydrophilic unstructured protein, highly soluble after boiling and with cryoprotectant activity. To clarify the physiological function of STRP, we characterized the phenotype and the response to low temperature stress of the strp knockout mutant. The mutation causes an equal impairment of plant growth and development both in physiological and cold stress conditions. The strp mutant is more susceptible to oxidative damage respect to the wild type, showing increased lipid peroxidation and altered membrane integrity. Furthermore, the analysis of Abscisic acid (ABA) effects on protein levels demonstrated that the hormone induces the increase of STRP levels, an effect in part ascribable to its ability to activate STRP expression. ABA treatments showed that the strp mutant displays an ABA hyposensitive phenotype in terms of seed germination, root development, stomata closure and in the expression of ABA-responsive genes. In conclusion, our results demonstrate that STRP acts as a multifunctional protein in the response mechanisms to low temperature, suggesting a crucial role for this protein in stress perception and in the translation of extracellular stimuli in an intracellular response
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