Thermodynamic Stability of Potassium-beta-Alumina

The activity of K sub 2 O in a mixture of alpha -alumina and potassium beta -alumina has been determined using a solid state galvanic cell in the temperature range 600-1000K. The cell is written such that the right hand electrode is positive. The solid electrolyte consisted of a dispersion of alpha -alumina ( approx 15 vol.%) in a matrix of K beta -alumina. The emf of the cell was found to be reversible and to vary linearly with temperature. From the emf and auxiliary data on In sub 2 O sub 3 and K sub 2 O from the literature, the activity of K sub 2 O in the two-phase mixture is obtained. The standard free energy of formation of K beta -alumina from component oxides is given. Graphs.

Non-enzymatic Degradation of (1→3)(1→4)-β-D-glucan in Aqueous Processing of Oats

Cereal water-soluble β-glucan [(1→3)(1→4)-β-D-glucan] has well-evidenced health benefits and it contributes to the texture properties of foods. These functions are characteristically dependent on the excellent viscosity forming ability of this cell wall polysaccharide. The viscosity is affected by the molar mass, solubility and conformation of β-glucan molecule, which are further known to be altered during food processing. This study focused on demonstrating the degradation of β-glucan in water solutions following the addition of ascorbic acid, during heat treatments or high pressure homogenisation. Furthermore, the motivation of this study was in the non-enzymatic degradation mechanisms, particularly in oxidative cleavage via hydroxyl radicals. The addition of ascorbic acid at food-related concentrations (2-50 mM), autoclaving (120°C) treatments, and high pressure homogenisation (300-1000 bar) considerably cleaved the β-glucan chains, determined as a steep decrease in the viscosity of β-glucan solutions and decrease in the molar mass of β-glucan. The cleavage was more intense in a solution of native β-glucan with co-extracted compounds than in a solution of highly purified β-glucan. Despite the clear and immediate process-related degradation, β-glucan was less sensitive to these treatments compared to other water-soluble polysaccharides previously reported in the literature. In particular, the highly purified β-glucan was relatively resistant to the autoclaving treatments without the addition of ferrous ions. The formation of highly oxidative free radicals was detected at the elevated temperatures, and the formation was considerably accelerated by added ferrous ions. Also ascorbic acid pronounced the formation of these oxidative radicals, and oxygen was simultaneously consumed by ascorbic acid addition and by heating the β-glucan solutions. These results demonstrated the occurrence of oxidative reactions, most likely the metal catalysed Fenton-like reactions, in the β-glucan solutions during these processes. Furthermore, oxidized functional groups (carbonyls) were formed along the β-glucan chain by the treatments, including high pressure homogenisation, evidencing the oxidation of β-glucan by these treatments. The degradative forces acting on the particles in the high pressure homogenisation are generally considered to be the mechanical shear, but as shown here, carbohydrates are also easily degraded during the process, and oxidation may have a role in the modification of polysaccharides by this technique. In the present study, oat β-glucan was demonstrated to be susceptible to degradation during aqueous processing by non-enzymatic degradation mechanisms. Oxidation was for the first time shown to be a highly relevant degradation mechanism of β-glucan in food processing.

Synthesis Of (+/-)-Beta-Cuparenone Via 3-Oxa-Beta-Cuparenone

Grignard reaction followed by ozonolysis, or ozonolysis followed by Grignard reaction on the pentenoate 8, generates the diol 9. Cyclodehydration of 9 leads to the 3-oxacuparene (6), whereas PCC oxidation furnishes the 3-oxa-beta-cuparenone (7). Methanesulfonic acid-P2O5 transforms 7 into cyclopentenones 4, 5, known precursors to beta-cuparenone (3), and the naphthalenone 14.

The effects of beta-mercaptoethanol and sodium dodecyl sulfate on the Humicola insolens beta-glucosidase

Hydrolysis of p-nitrophenyl-beta-D-glucoside by the beta-glucosidase of a thermophilic and cellulolytic fungus, Humicola insolens was stimulated by two-fold in the presence of high concentrations of beta-mercaptoethanol. This enzyme did not have any free sulfhydryl groups and high concentrations of beta-mercaptoethanol (5% v/v) reduced all of the three disulfide bonds present in the enzyme. In contrast, the hydrolysis of cellobiose and cellulose polymers was inhibited by 50% under the same conditions. Sodium dodecyl sulfate (1% w/v) even in combination with beta-mercaptoethanol did not show any significant effects on this enzyme. These unusual properties suggest that this enzyme may be of significant importance for understanding the structure of the enzyme.

The identification of 14 alpha,17 beta-dihydroxyandrost-4-en-3-one monohydrate and 14 alpha,17 beta-dihydroxyandrosta-1,4-dien-3-one monohydrate, metabolites of androstenedione in Mucor piriformis

The microorganism Mucor piriformis transforms androst-4-ene-3,17-dione into a major and several minor metabolites. X-ray crystallographic analysis of two of these metabolites was undertaken to determine unambiguously their composition and chirality. Crystals belong to the orthorhombic space-group P2(1)2(1)2(1), with a = 7.199(4) angstrom and a = 6.023(3) angstrom, b = 11.719(3) angstrom and b = 13.455(4) angstrom, c = 20.409(3) angstrom and c = 20.702(4) angstrom for the two title compounds, respectively. The structures have been refined to final R values of 0.060 and 0.040, respectively.

Ability of human chorionic gonadotropin beta-subunit to inhibit the steroidogenic response to lutropin.

Ability of the beta-subunit of human chorionic gonadotropin to inhibit the response to lutropin (luteinizing hormone, LH) was tested in the immature rat ovarian system and pregnant-mare-serum-gonadotropin-primed rat ovarian system with progesterone production being used as the response. Human chorionic gonadotropin beta-subunit was found to inhibit human and ovine lutropin-stimulated progesterone production. At a constant dose of lutropin, inhibition was dependent on the concentration of beta-subunit. When concentration of the beta-subunit was kept constant at 5.0 microgram/ml and the concentration of lutropin was varied, the inhibition was maximum at the saturating concentration of the native hormone. The alpha-subunit of the human chorionic gonadotropin did not inhibit the response to lutropin. The lutropin/beta-subunit ratio required to produce an inhibition of response was much lower than that required to bring about an observable inhibition of binding.

Biochemical and structural characterization of recombinant hyoscyamine 6 beta-hydroxylase from Datura metel L.

Hyoscyamine 6 beta-hydroxylase (H6H; EC 1.14.11.11), an important enzyme in the biosynthesis of tropane alkaloids, catalyzes the hydroxylation of hyoscyamine to give 6 beta-hydroxyhyoscyamine and its epoxidation in the biosynthetic pathway leading to scopolamine. Datura metel produces scopolamine as the predominant tropane alkaloid. The cDNA encoding H6H from D. mete! (DmH6H) was cloned, heterologously expressed and biochemically characterized. The purified recombinant His-tagged H6H from D. mete! (DmrH6H) was capable of converting hyoscyamine to scopolamine. The functionally expressed DmrH6H was confirmed by HPLC and ESI-MS verification of the products, 6 beta-hydroxyhyoscyamine and its derivative, scopolamine; the DmrH6H epoxidase activity was low compared to the hydroxylase activity. The K-m values for both the substrates, hyoscyamine and 2-oxoglutarate, were 50 mu M each. The CD (circular dichroism) spectrum of the DmrH6H indicated a preponderance of alpha-helicity in the secondary structure. From the fluorescence studies, Stern-Volmer constants for hyoscyamine and 2-oxoglutarate were found to be 0.14 M-1 and 0.56 M-1, respectively. These data suggested that the binding of the substrates, hyoscyamine and 2-oxoglutarate, to the enzyme induced significant conformational changes. (C) 2010 Elsevier Masson SAS. All rights reserved.