pH Stability (ph + stability)

Distribution by Scientific Domains


Selected Abstracts


Purification and partial characterization of glutathione S -transferase from insecticide-resistant field populations of Liposcelis paeta Pearman (Psocoptera: Liposcelididae)

ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY (ELECTRONIC), Issue 2 2009
Shuang Wu
Abstract Enzymes that possess glutathione S-transferase (GST) activity were purified to homogeneity by glutathione-agarose affinity chromatography from three field populations of Liposcelis paeta (Pearman). These populations were collected from Nanyang city of Henan Province (NY), Wuzhou (WZ) and Hezhou (HZ) cities of Guangxi Province, China, and had different susceptibilities to dichlorvos [LC50s of the NY (281.48,mg/m2), the WZ (285.07,mg/m2), and the HZ (243.52,mg/m2), respectively]. The specific activities of purified enzymes from these three populations increased 32.24-, 99.81-, and 42.52-fold, respectively. Kinetic analyses showed that the catalytic activity of purified GST from NY population towards GSH was much higher than the others, while WZ population reached the highest in V. SDS,polyacrylamide electrophoresis revealed that the purified GST had two subunits with a molecular mass of 23.31 and 20.43,kDa for NY, 53.14 and 20.13,kDa for WZ, and 50.79 and 19.42,kDa for HZ, respectively. The in vitro inhibition studies of GSTs indicated that three kinds of insecticides (chlorpyrifos, carbosulfan, and cypermethrin) and five metallic ions (Zn2+, Ba2+, Ca2+, Hg2+, Mn2+, and Mg2+) all possessed inhibitory effects on purified GST, and ethacrynic acid (EA, a specific inhibitor of GST) expressed inhibitory effects. In the bioassay, three populations of L. paeta had different susceptibilities to different insecticides, even after they were reared on diets consisting of 25% EA. The GST activities of L. paeta from different areas also showed different temperature and pH stabilities. The differences in GST among the three populations may be attributed partially to the differences in control practices for psocids between Henan and Guangxi Provinces. © 2009 Wiley Periodicals, Inc. [source]


Cell-surface phytase on Pichia pastoris cell wall offers great potential as a feed supplement

FEMS MICROBIOLOGY LETTERS, Issue 1 2010
Piyanun Harnpicharnchai
Abstract Cell-surface expression of phytase allows the enzyme to be expressed and anchored on the cell surface of Pichia pastoris. This avoids tedious downstream processes such as purification and separation involved with extracellular expression. In addition, yeast cells with anchored proteins can be used as a whole-cell biocatalyst with high value added. In this work, the phytase was expressed on the cell surface of P. pastoris with a glycosylphosphatidylinositol anchoring system. The recombinant phytase was shown to be located at the cell surface. The cell-surface phytase exhibited high activity with an optimal temperature at 50,55 °C and two optimal pH peaks of 3 and 5.5. The surface-displayed phytase also exhibited similar pH stability and pepsin resistance to the native and secreted phytase. In vitro digestibility test showed that P. pastoris containing cell-surface phytase released phosphorus from feedstuff at a level similar to secreted phytase. Yeast cells expressing phytase also provide additional nutrients, especially biotin and niacin. Thus, P. pastoris with phytase displayed on its surface has a great potential as a whole-cell supplement to animal feed. [source]


Cross-Linked Enzyme Aggregates of Chloroperoxidase: Synthesis, Optimization and Characterization

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009
Daniel
Abstract In this study we have optimized the conditions to precipitate and cross-link the enzyme chloroperoxidase (EC,1.11.1.10) from Caldariomyces fumago (CPO) using 1,2-dimethoxyethane as the precipitating agent. The coprecipitation of the enzyme with albumin and pentaethylenehexamine was needed for optimum results, presumably due to the low number of lysines available in CPO. The enzyme was immobilized with an activity recovery of 68%. The cross-linked enzyme aggregate showed higher temperature and pH stability, and better hydrogen peroxide tolerance than the free enzyme. [source]


Muscle fibre types and size distribution in sub-antarctic notothenioid fishes

JOURNAL OF FISH BIOLOGY, Issue 6 2000
D. A. Fernandez
The presumptive tonic muscles fibres of Cottoperca gobio, Champsocephalus esox, Harpagifer bispinis, Eleginops maclovinus, Patagontothen tessellata, P. cornucola and Paranotothenia magellanica stained weakly or were unstained for glycogen, lipid, succinic dehydrogenase (SDHase) and myosin ATPase (mATPase) activity. Slow, intermediate and fast twitch muscle fibres, distinguished on the basis of the pH stability of their mATPases, showed intense, moderate and low staining activity for SDHase, respectively. Slow fibres were the major component of the pectoral fin adductor profundis muscle. The proportion of different muscle fibre types varied from the proximal to distal end of the muscle, but showed relatively little variation between species. The myotomes contained a lateral superficial strip of red muscle composed of presumptive tonic, slow twitch and intermediate fibres, thickening to a major wedge at the horizontal septum. All species also had characteristic secondary dorsal and ventral wedges of red muscle. The relative abundance and localization of muscle fibre types in the red muscle varied between species and with body size in the protandric hermaphrodite E. maclovinus. The frequency distribution of diameters for fast twitch muscle fibres, the major component of deep white muscle, was determined in fish of a range of body sizes. The absence of fibres <20 ,m diameter was used as a criterion for the cessation of muscle fibre recruitment. Fibre recruitment had stopped in P. tessellata of 13·8 cm LT and E. maclovinus of 32·8 cm LT, equivalent to 49 and 36·5% of their recorded maximum sizes respectively. As a result in 20-cm P. tessellata, the maximum fibre diameter was 300 ,m and 36% of fibres were in excess of 200 ,m. The unusually large maximum fibre diameter, the general arrangement of the red muscle layer and the extreme pH lability of the mATPase of fast twitch fibres are all common characters of the sub-Antarctic and Antarctic Notothenioids, including Cottoperca gobio, the suggested sister group to the Notothenidae. [source]


Architecture and performance of mesoporous silica-lipase hybrids via non-covalent interfacial adsorption

AICHE JOURNAL, Issue 2 2010
Shan Lu
Abstract To investigate the effects of surface property of mesoporous supports on the lipase immobilization and the performance of immobilized lipase, the mesoporous molecular sieve SBA-15 is functionalized with three organic moieties, dimethyl (DM), diisopropyl (DIP), and diisobutyl (DIB), respectively, by post-synthesis grafting and one-pot synthesis methods. Porcine pancreas lipase (PPL) is immobilized on SBA-15 supports through hydrogen bonding and hydrophobic interaction. The hydrophobic adsorption involves no active sites of PPL, and neither hyper-activation nor total inactivation occurs. The study on the intrinsic stability of PPL, including thermal stability, pH stability, and storage stability, indicates that the entrapment in mesoporous supports, and especially in organic-functionalized supports, makes PPL more resistant to temperature increment but more sensitive to pH change. The reusability investigation shows that the organic modification of mesoporous surface inhibits the enzyme leaching to some extent, resulting in a better operational stability. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Preparation of trypsin-immobilised chitosan beads and their application to the purification of soybean trypsin inhibitor

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 13 2008
Li Zhang
Abstract BACKGROUND: Trypsin inhibitors are among the most important antinutritional factors in legumes. Recent research has shown that soybean trypsin inhibitor (SBTI) exhibits multiple bioactivities, but very few studies on the purification of SBTI are available. Enzymes are commonly used as biospecific ligands in affinity purification of their substrates or inhibitors. The aim of the present study was to prepare trypsin (EC 3.4.21.4)-immobilised chitosan beads and use them to purify trypsin inhibitor from soybean whey. RESULTS: Compared with free trypsin, the immobilised trypsin had higher thermal and pH stability. The adsorption ratio of SBTI from crude SBTI aqueous solution by trypsin-immobilised chitosan beads was 33.3%. The purified SBTI obtained by affinity chromatography was characterised by sodium dodecyl sulfate polyacrylamide gel electrophoresis as a single polypeptide band with an Mr of 8.3 kDa belonging to the Bowman,Birk family. CONCLUSION: Trypsin-immobilised chitosan beads were effectively used in the affinity separation of trypsin inhibitor from soybean seeds, thus indicating that immobilised trypsin may have practical application in the soybean-processing industry. The results of this study provide a background for further investigation of potential applications of soybean bioactive constituents in the areas of agriculture and food. Copyright © 2008 Society of Chemical Industry [source]


Multiple virulence factors of Cryptococcus neoformans are dependent on VPH1

MOLECULAR MICROBIOLOGY, Issue 4 2001
Todd Erickson
Acidification of vesicular compartments plays an important role in a number of cellular transport processes, including protein secretion, metal cofactor insertion, glycosylation and pH stability. In the present study, we identify and characterize a component of the vesicular proton pump, Vph1p, to determine its role in the virulence of the AIDS-related fungal pathogen Cryptococcus neoformans. Insertional mutagenesis and plasmid rescue were used to identify the VPH1 gene by screening for mutants defective in laccase activity. Disruption of VPH1 resulted in defects in three virulence factors (capsule production, laccase and urease expression), as well as a growth defect at 37°C, but only a small growth reduction at 30°C. These effects were duplicated by the vacuolar (H+)-ATPase inhibitor bafilomycin A1. Furthermore, the vph1 insertional mutant was also avirulent in a mouse meningo-encephalitis model. Complementation of the insertional mutant with wild-type VPH1 resulted in a recovery of virulence factor expression, normal growth at 37°C and restoration of full virulence. These studies establish the importance of the VPH1 gene and vesicular acidification in the virulence of C. neoformans. [source]


Use of Co-Immobilized ,-Amylase and Pullulanase in Reduction of Saccharification Time of Starch and Increase in Maltose Yield

BIOTECHNOLOGY PROGRESS, Issue 3 2003
K. S. Atia
,-Amylase and pullulanase were co-immobilized to poly(acrylamide-acrylic acid) resin [P(AAm-AAc)] using 1-ethyl-3,(3-dimethylaminopropyl) carbodimide hydrochloride (EDC). The combined ,-amylase and pullulanase activity was 32% relative to the nonimmobilized ,-amylase. Co-immobilization of ,-amylase and pullulanase increased the maltose yield compared to thart of the immobilized ,-amylase alone and reduced the saccharification time to about 50 h. The results showed that there is a significant increase in the thermal stability, pH stability, and stability toward , irradiation. The results also suggest that the co-immobilization of ,-amylase and pullulanase is a potentially useful approach for commercial starch hydrolysis. [source]