D-mannose transport and metabolism in isolated enterocytes

D-mannose transport and metabolism has been studied in enterocytes isolated from chicken small intestine. In the presence of Na(+), the mannose taken up by the cells either remains free, is phosphorylated, is catabolized to H(2)O, or becomes part of membrane components. The mannose remaining free in the cytosol is released when the cells are transferred to an ice bath. The Na(+)-dependent D-mannose transport is electrogenic and inhibited by ouabain and dinitrophenol; its substrate specificity differs from SGLT-1 transporter. The Glut2 transporter inhibitors phloretin and cytochalasin B added following 30-min mannose uptake reduced the previously accumulated D-mannose, whereas these two agents increased the cell to external medium 3-O-methyl-glucose (3-OMG) concentration ratio. D-mannose efflux rate from preloaded D-[2-(3)H]-mannose enterocytes is Na(+)-independent. Phloretin did not affect D-mannose efflux rate, whereas it inhibited that of 3-OMG. Neither mannose uptake nor efflux rate were affected by fructose. It is concluded that part of the mannose taken up by the enterocytes is rapidly metabolized and that enterocytes have two D- mannose transport systems: one is concentrative and Na(+)-dependent and the other is Na(+)-independent and passive.     

Integrated biodiesel production: a comparison of different homogeneous catalysts systems

The most common catalysts for biodiesel production are homogeneous basic catalysts. In the present paper, a comparison is made of different basic catalysts (sodium methoxide, potassium methoxide, sodium hydroxide and potassium hydroxide) for methanolysis of sunflower oil. All the reactions were carried out under the same experimental conditions in a batch stirred reactor and the subsequent separation and purification stages in a decanter. The analytical methods included gas chromatography and the determination of fat and oil conventional parameters. The biodiesel purity was near 100 wt.% for all catalysts. However, near 100 wt.% biodiesel yields were only obtained with the methoxide catalysts. According to the material balance of the process, yield losses were due to triglyceride saponification and methyl ester dissolution in glycerol. Obtained biodiesel met the measured specifications, except for the iodine value, according to the German and EU draft standards. Although all the transesterification reactions were quite rapid and the biodiesel layers achieved nearly 100% methyl ester concentrations, the reactions using sodium hydroxide turned out the fastest.     

Light-induced absorption spectra of the D1–D2–cytochrome b 559 complex of Photosystem II: Effect of methyl viologen concentration

The light-induced difference absorption spectra associated to the photo-accumulation of reduced pheophytin a were studied in the isolated D1–D2–Cyt b559 complex in the presence of variable methyl viologen concentrations and different illumination conditions under anaerobiosis. Depending on the methyl viologen/reaction centre ratio, the relative intensities of the spectral bands at 681.5±0.5, 667.0±0.5 and 542.5±0.5 nm were modified. The reduced pheophytin a located at the D1-branch of the complex absorbs at 681.7±0.5 nm, and at least two additional pigment species contribute to the Q_y band of the difference absorption spectra with maxima at 667.0±0.5 and 680.5±0.5 nm. We propose the additional species correspond to a peripheral chlorophyll a and the pheophytin a located at the D2-branch of the complex, respectively. The blue absorbing chlorophyll at 667 nm is susceptible to chemical redox changes with a midpoint reduction potential of +470 mV. The Q_x absorption bands of both pheophytins localised at the D2- and D1-branch of the D1–D2–Cyt b559 complex were at 540.7±0.5 and 542.9±0.5, respectively. The results indicated that the two pheophytin molecules can be photoreduced in the D1–D2–Cyt b559 complex in certain experimental conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cytosolic glutamine synthetase and not nitrate reductase from the green alga Chlamydomonas reinhardtii is phosphorylated and binds 14-3-3 proteins

 The nitrate reductase activity from Chlamydomonas reinhardtii was not altered when extracts were incubated with yeast 14-3-3 proteins in the presence of Mg-ATP. However, the C. reinhardtii extracts contained 14-3-3 proteins capable of inhibiting the spinach nitrate reductase, raising the question of their physiological substrates. Two C. reinhardtii proteins of about 48 and 35 kDa were eluted from 14-3-3 affinity chromatography columns and bound to 14-3-3s in overlay assays. The 48-kDa protein corresponded to the cytosolic isoform of glutamine synthetase (GS1). The GS1 was phosphorylated by a Ca²⁺- and calmodulin-dependent protein kinase partially purified from the alga. However, neither phosphorylation nor 14-3-3 binding seemed to change GS catalytic activity. Received: 3 February 2000 / Accepted: 6 May 2000     

Design and synthesis of S-(-)-2-[[4-(napht-1-yl)piperazin-1-yl]methyl]-1,4-dioxoperhydropyrrolo[1,2-a]pyrazine (CSP-2503) using computational simulation. A 5-HT1A receptor agonist

Based on a computational model for 5-HT(1A)R-ligand interaction and QSAR studies, we have designed and synthesized a new series of arylpiperazines 2-8 which exhibit high 5-HT(1A)R affinity and selectivity over alpha(1)-adrenergic receptors. Among them, compound CSP-2503 (4) has been pharmacologically characterized as a 5-HT(1A)R agonist at somatodendritic and postsynaptic sites, endowed with anxiolytic properties.     

Dermatoglyphic variation in Spanish Basque populations

The present study involves the evaluation of digital dermatoglyphic traits of 2185 unrelated individuals (1152 females and 1033 males) from 17 natural valleys of the four Basque provinces (Vizcaya, Guipúzcoa, Navarra, and Alava) in the Spanish Basque Country. Univariate intervalley and between-sex comparisons were carried out by means of chi-square contingency analysis for pattern types and by means of one-way analysis of variance for ridge counts. Multivariate intervalley comparison was carried out by means of correspondence analysis for pattern types and by principal component analysis for ridge counts. The results of this study are notable for the following findings: (1) in general, all variables are significantly heterogeneous among valley populations; (2) there was a greater differentiation among the valley populations than between sexes in one valley population; (3) affinities among the intervalley populations depend on the variables considered; (4) the valley populations from Vizcaya resemble those from the Pyrenees; (5) based on interprovince comparisons, the Vizcaya and Navarra samples are the closest: (6) in general, the valley samples from Alava are the worst clustered; (7) the universality of dermatoglyphic component structure fits better in males.     

The inhibition of semicarbazide-sensitive amine oxidase by aminohexoses

Semicarbazide-sensitive amine oxidase (EC 1.4.3.6; amine:oxygen oxidoreductase (deaminating) (copper-containing); SSAO) is a multifunctional protein. It acts under inflammatory conditions as a vascular-adhesion protein (VAP-1), mediating the adhesion of lymphocytes to vascular endothelial cells. The relationships, if any, between this adhesion function and the enzymatic functions (amine-substrate specificity and catalysis) of SSAO have not yet been defined. Since cell surface amino sugars and their derivatives are known to be involved in cell-to-cell recognition, we have investigated their possible effects on the enzyme activity of SSAO. The aminohexoses galactosamine, glucosamine and mannosamine were not oxidatively deaminated by SSAO. However, their presence during the assay of benzylamine oxidation resulted in a time-dependent inhibition. This inhibition was shown to follow saturation kinetics with respect to hexosamine concentration. Although time-dependent, the inhibition of SSAO activity was found to be reversible by dilution. In contrast, there is no such inhibition when the N-acetylamino sugar derivatives or the parent sugars (galactose, glucose and mannose) replaced the amino sugars in the reaction mixture. These results suggest that the interactions between SSAO and aminohexoses are specific and, therefore, that the cell-adhesion functions and amine-recognition functions of VAP-1/SSAO may be interlinked.     

Semicarbazide-sensitive amine oxidases in pig dental pulp

The behaviour of semicarbazide-sensitive amine oxidase (SSAO; E.C. 1.4.3.6) in dental pulp has been studied, with particular reference to the metabolism of 5-hydroxytryptamine (5-HT; serotonin). Kinetic studies using radioactively labelled substrates have confirmed benzylamine, 2-phenylethylamine (PEA) and 5-HT to be substrates for microsomal SSAO from porcine dental pulp. Kinetic substrate-competition studies indicated the presence of two forms of SSAO in dental pulp; one that oxidises benzylamine and PEA but not 5-HT and a second that oxidises 5-HT and PEA but not benzylamine. These two forms also differ in their thermostabilities at 60 and 70 degrees C, although this thermal inactivation is partly reversible.     

Glyceraldehyde-3-phosphate dehydrogenase,a glycolytic enzyme present in the periplasm of Aeromonas hydrophila

This is the first report describing the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), as a protein associated with the cell envelope of a gram-negative bacterium (Aeromonas hydrophila). Dose-dependent GAPDH activity was detected in whole bacterial cells from exponentially growing cultures, indicating that an active form of GAPDH is located outside the plasma membrane. This activity represents roughly 10–20% of total cell activity, and it is not reduced by pretreatment of the cells with trypsin. Assays with soluble GAPDH indicate that the activity measured in intact cells does not originate by rebinding to intact cells of cytosolic enzyme released following cell lysis. GAPDH activity levels detected in intact cells varied during the growth phase. The relationship between GAPDH activity and cell culture density was not linear, showing this activity as a major peak in the late-logarithmic phase (A₆₀₀ = 1.1–1.3), and a decrease when cells entered the stationary phase. The late exponential growing cells showed a GAPDH activity 3 to 4-fold higher than early growing or stationary cells. No activity was detected in culture supernatants. Enzymatic and Western-immunoblotting analysis of subcellular fractions (cytosol, whole and outer membranes, and periplasm) showed that GAPDH is located in the cytosol, as expected, and also in the periplasm. These results place the periplasmic GAPDH of A. hydrophila into the family of multifunctional microbial cell wall-associated GAPDHs which retain their catalytic activity. This revised version was published online in June 2006 with corrections to the Cover Date.