Ruminant animals depend on cellulolytic ruminal bacteria to digest cellulose, but these bacteria cannot resist the low ruminal pH that modern feeding practices can create. Because the cellulolytic bacteria cannot grow on cellobiose at low pH, pH sensitivity is a general aspect of growth and not just a limitation of the cellulases per se. Acid-resistant ruminal bacteria have evolved the capacity to let their intracellular pH decrease, maintain a small pH gradient across the cell membrane, and prevent an intracellular accumulation of VFA anions. Cellulolytic bacteria cannot grow with a low intracellular pH, and an increase in pH gradient leads to anion toxicity. Prevotella ruminicola cannot digest native cellulose, but it grows at low pH and degrades the cellulose derivative, carboxymethylcellulose. The Prevotella ruminicola carboxymethylcellulase cannot bind to cellulose, but a recombinant enzyme having the Prevotella ruminicola catalytic domain and a binding domain from Thermomonspora fusca was able to bind and had cellulase activity that was at least 10-fold higher. Based on these results, gene reconstruction offers a means of converting Prevotella ruminicola into a ruminal bacterium that can digest cellulose at low pH.
The surface properties of a well-crystallized synthetic goethite have been studied by acid-base potentiometric titrations, electrophoresis, and phosphate and arsenate adsorption isotherms at different pH and electrolyte concentrations. The PZC and IEP of the studied goethite were 9.3+/-0.1 and 9.3+/-0.2, respectively. Phosphate and arsenate adsorption decrease as the pH increases in either 0.1 or 0.01 M KNO(3) solutions. Phosphate adsorption is more sensitive to changes in pH and ionic strength than that of arsenate. The combined effects of pH and ionic strength result in higher phosphate adsorption in acidic media at most ionic strengths, but result in lower phosphate adsorption in basic media and low ionic strengths. The CD-MUSIC model yields rather good fit of the experimental data. For phosphate it was necessary to postulate the presence of three inner-sphere surface complexes (monodentate nonprotonated, bidentate nonprotonated, and bidentate protonated). In contrast, arsenate could be well described by postulating only the presence of the two bidenate species. A small improvement of the arsenate adsorption data could be achieved by assuming the presence of a monodentate protonated species. Model predictions are in agreement with spectroscopic evidence, which suggest, especially for the case of arsenate, that mainly bidentate inner-sphere complexes are formed at the goethite-water interface.
Membrane and nuclear proteins of poor solubility have been separated by high resolution two‐dimensional (2‐D) gel electrophoresis. Isoelectric focusing with immobilized pH gradients leads to severe quantitative losses of proteins in the resulting 2‐D map, although the resolution is usually high. Protein solubility could be improved by using denaturing solutions containing various detergents and chaotropes. Best results were obtained with a denaturing solution containing urea, thiourea, and detergents (both nonionic and zwitterionic). The usefulness of thiourea‐containing denaturing mixtures is shown for microsomal and nuclear proteins as well as for tubulin, a protein highly prone to aggregation.
AbstractThe pH‐sensitive polymeric materials are the current need of time in targeted drug delivery applications. The pH‐sensitive cross‐linked psyllium grafted‐poly (acrylonitrile‐co‐acrylic acid) [Psy‐g‐Poly (An‐co‐AA)] was synthesized by using ceric ammonium nitrate (CAN) redox initiator via chemical grafting process for colon cancer treatment. The synthesized material [Psy‐g‐Poly (An‐co‐AA)] was characterized by nuclear magnetic resonance, Fourier transform infrared, scanning electron microscopy, X‐ray diffraction Zeta potential, and thermal gravimetric analysis. Furthermore, quercetin (QPN) drug was encapsulated in cross‐linked grafted psyllium preparing nanoparticles of encapsulated QPN via the sonication technique for controlled release of QPN and testing of in vitro anticancer and antioxidant activities. The anticancer activity of QNP and QPN were studied on human cell line (HCT‐15) and it was observed that QNP also exhibited excellent anticancer and antioxidant activity as compared to only QPN. QNP showed maximal swelling at pH‐7 and demonstrated maximum QPN release (93%) at the pH of the intestinal fluid (pH‐7.4). The drug release kinetic data followed the Korsmeyer–Peppas model (R2 = 0.9808) kinetic model, indicating the mechanism of drug release from QNP was non‐Fickian diffusion. Furthermore, pH‐specific QPN release behavior of Psy‐g‐Poly (An‐co‐AA) can be utilized for colon targeted drug delivery.