Purification, immobilization and characterization of tannase from Penicillium variable

Tannase from Penicillium variable IARI 2031 was purified by a two-step purification strategy comprising of ultra-filtration using 100 kDa molecular weight cutoff and gel-filtration using Sephadex G-200. A purification fold of 135 with 91% yield of tannase was obtained. The enzyme has temperature and pH optima of 50 degrees C and 5 degrees C, respectively. However, the functional temperature range is from 25 to 80 degrees C and functional pH range is from 3.0 to 8.0. This tannase could successfully be immobilized on Amberlite IR where it retains about 85% of the initial catalytic activity even after ninth cycle of its use. Based on the Michaelis-Menten constant (Km) of tannase, tannic acid is the best substrate with Km of 32 mM and Vmax of 1.11 micromol ml(-1)min(-1). Tannase is inhibited by phenyl methyl sulphonyl fluoride (PMSF) and N-ethylmaleimide retaining only 28.1% and 19% residual activity indicating that this enzyme belongs to the class of serine hydrolases. Tannase in both crude and crude lyophilized forms is stable for one year retaining more than 60% residual activity.     

Physico-Chemical Characterization of Watermelon Urease upon Immobilization in Alginate Beads

Watermelon (Citrullus vulgaris) urease was immobilized in 3.5% alginate leading to 72% immobilization. There was no leaching of the enzyme over a period of 15 days at 4°C. It continued to hydrolyse urea at a faster rate upto 90 min of incubation. The immobilized urease exhibited a shift of apparent pH optimum by one unit towards acidic side (from pH 8.0 to 7.0). The K_m was found to be 13.3 mM; 1.17 times higher than the soluble enzyme (11.4 mM). The beads were fairly stable upto 50°C and exhibited activity even at ?10°C. The enzyme was significantly activated by ME and it exhibited two peaks of activation; one at lower concentration and another at higher concentration. Time-dependent ureolysis in presence of ME progressed at a much elevated rate. Unlike soluble enzyme, which was inhibited at 200 mM urea, the immobilized enzyme was inhibited at 600 mM of urea and above, and about 47% activity was retained at 2000 mM urea. Moreover, the inhibition caused by high urea concentration was partially abolished by ME. The significance of the observations is discussed.     

Immobilization of Xylan-Degrading Enzymes from Scytalidium thermophilum on Eudragit L-100

Summary Xylanase from Scytalidium thermophilum was immobilized on Eudragit L-100, a pH sensitive copolymer of methacrylic acid and methyl methacrylate. The enzyme was non-covalently immobilized and the system expressed 70% xylanase activity. The immobilized preparation had broader optimum temperature of activity between 55 and 65 °C as compared to 65 °C in case of free enzyme and broader optimum pH between 6.0 and 7.0 as compared to 6.5 in case of free enzyme. Immobilization increased the t_1/2 of enzyme at 60 °C from 15 to 30 min with a stabilization factor of 2. The K_m and V_max values for the immobilized and free xylanase were 0.5% xylan and 0.89 μmol/ml/min and 0.35% xylan and 1.01 μmol/ml/min respectively. An Arrhenius plot showed an increased value of activation energy for immobilized xylanase (227 kcal/mol) as compared to free xylanase (210 kcal/mol) confirming the higher temperature stability of the free enzyme. Enzymatic saccharification of xylan was also improved by xylanase immobilization.     

Inhibition of Water Melon (Citrullus vulgaris) Urease by Fluoride

Effect of fluoride on the activity of purified urease from seeds of watermelon (Citrullus vulgaris) was studied. Fluoride exhibited a concentration dependent inhibition both in presenceand absence ofthe substrate. The inhibition was non-competitive. Addition of 8mM β-mercaptoethanol gradually abolished the fluoride inhibition. β-mnercaptoethanol, in presence of fluoride, also exhibited a concentration dependent suppression of inhibition caused by fluoride. The significance of these observations is discussed.     

D-Aspartate oxidase and D-amino acid oxidase are localised in the peroxisomes of terrestrial gastropods

D-Aspartate oxidase and D-amino acid oxidase were found in high activity in the tissues of representative species of terrestrial gastropods. Analytical subcellular fractionation demonstrated that both of these oxidases co-localised with the peroxisome markers, acyl-CoA oxidase and catalase, in the digestive gland homogenate. Electron microscopy of peak peroxisome fractions showed particles of uniform size with generally well preserved variably electron-dense matrices bounded by an apparently single limiting membrane. Many of the particles exhibited a core region of enhanced electron density. Catalase cytochemistry of peak fractions confirmed the peroxisome identity of the organelles. Peroxisome-enriched subcellular fractions were used to investigate the properties of gastropod D-aspartate oxidase and D-amino acid oxidase activities. The substrate and inhibitor specificities of the two activities demonstrated that two distinct enzymes were present analogous to, but not identical to, the equivalent mammalian peroxisomal enzymes.     

Volatile fatty acid production during anaerobic mesophilic digestion of tea and vegetable market wastes

Extraction of the organic content from vegetable market waste and tea waste was carried out in a packed digester for 24 and 300 h respectively. The sequence of appearance of volatile fatty acids during digestion of both the substrates was found to be different. The sequence was (Acetic, Propionic) > (Isobutyric, Butyric) > Valeric for digestion of vegetable market waste while it was Isovaleric > (Isobutyric, Acetic) > Propionic during digestion of tea waste. During the course of digestion, the early appearance of an acid did not relate to its high concentration. The rate of production of acetic acid and propionic acid was found to be higher than other volatile acids during digestion of both the substrates, although it was approximately ten times higher for vegetable market waste compared to tea waste. The acids can be arranged in four groups according to their rate of production as Acetic > Propionic > Butyric > (Valeric, Isobutyric) for vegetable market waste and Acetic > Isobutyric > Isovaleric > Propionic for tea waste.     

Elucidation of the anticancer potential and tubulin isotype-specific interactions of β-sitosterol

Beta-sitosterol (β-SITO), a phytosterol present in many edible vegetables, has been reported to possess antineoplastic properties and cancer treatment potential. We have shown previously that it binds at a unique site (the ‘SITO-site’) compared to the colchicine binding site at the interface of α- and β-tubulin. In this study, we investigated the anticancer efficacy of β-SITO against invasive breast carcinoma using MCF-7 cells. Since ‘isotypes’ of β-tubulin show tissue-specific expression and many are associated with cancer drug resistance, using computer-assisted docking and atomistic molecular dynamic simulations, we also examined its binding interactions to all known isotypes of β-tubulin in αβ-tubulin dimer. β-SITO inhibited MCF-7 cell viability by up to 50%, compared to vehicle-treated control cells. Indicating its antimetastatic potential, the phytosterol strongly inhibited cell migration. Immunofluorescence imaging of β-SITO-treated MCF-7 cells exhibited disruption of the microtubules and chromosome organization. Far-UV circular dichroism spectra indicated loss of helical stability in tubulin when bound to β-SITO. Docking and MD simulation studies, combined with MM-PBSA and MM-GBSA calculations revealed that β-SITO preferentially binds with specific β-tubulin isotypes (β_II and β_III) in the αβ-tubulin dimer. Both these β-tubulin isotypes have been implicated in drug resistance against tubulin-targeted chemotherapeutics. Our data show the tubulin-targeted anticancer potential of β-SITO, and its potential clinical utility against β_II and β_III isotype-overexpressing neoplasms.