Sorensen's Phosphate Buffer pH Research Articles

Formulation and evaluation of piroxicam suppositories.

Piroxicam suppositories were prepared by using water soluble and oil soluble suppository bases. All the prepared suppositories were evaluated for various physical parameters like weight variation, drug content and hardness, melting point, disintegration and macromelting range. Invitro release study was performed USP type I apparatus using Sorensen's phosphate buffer pH 7.4 as dissolution media. The suppositories prepared with water soluble bases were within permissible range of all physical parameters. In vitro drug released from water soluble bases (hydrous PEG and anhydrous PEG) was greater than that from oil soluble bases. Keywords: Piroxicam; In vitro evaluation; Macromelting range; Water soluble bases; Suppositories

Ligand Binding Determines Whether CD46 Is Internalized by Clathrin-coated Pits or Macropinocytosis

CD46 is a ubiquitous human cell surface receptor for the complement components C3b and C4b and for various pathogens, including the measles virus and human herpes virus 6. Ligand binding to CD46 affects (i) protection of autologous cells from complement attack by breakdown of complement components, (ii) intracellular signals that affect the regulation of immune cell function, (iii) antigen presentation, and (iv) down-regulation of cell surface CD46. Recent evidence indicates that CD46 signaling can link innate and acquired immune function. The molecular mechanisms for these processes and the importance of intracellular trafficking of the receptor have not yet been elucidated. We demonstrate here that, in nonlymphoid cells, CD46 is constitutively internalized via clathrin-coated pits, traffics to multivesicular bodies, and is recycled to the cell surface. However, cross-linking of CD46 at the cell surface, by either multivalent antibody or by measles virus, induces pseudopodia that engulf the ligand in a process similar to macropinocytosis, and leads to the degradation of cell surface CD46. Thus, we have elucidated two pathways for CD46 internalization, which are regulated by the valence of cross-linking of CD46 and which utilize either clathrin-coated pits or pseudopodial extension. This has important implications for CD46 signaling, antigen presentation, CD46 down-regulation, and engulfment of pathogens.

BINDING OF PIPRINHYDRINATE TO PLASMA PROTEINS AND THEIR SUBSTITUTES

The binding of piprinhydrinate to bovine serum albumin (BSA) was studied in isotonic Sorensen's phosphate buffer pH 7.4 at 25±1°C, using equilibrium dialysis technique. Piprinhydrinate was bound to BSA and the plot was curved indicating the presence of morethan one binding site on the albumin molecule. At fixed protein concentration the percentage of bound drug to bovine serum albumin was inversely proportional to the concentration of the drug. But the binding parameters (binding constants as well as the number of binding sites) were found to be unaffected as the albumin concentration increased. However, binding parameters showed no significant difference due to pH change. Phosphate buffer, Gomori's tris-HCl buffer and Walpole's acetate buffer have different effect on the binding of piprinhydrinate to BSA; the values of the binding parameters can be arranged as follows: Sorensen's phosphate buffer > Gomori's tris-HCl > Walpole's acetate buffer. Also, it was found that chloride ions decrease the amount of the drug bound to BSA. The interaction of the drug with dextrans (40000, 266000 and 500000) in isotonic Sorensen's buffer pH 7.4 was investigated. No interaction was observed between the drug and the tested dextrans under the condition of the experiment. Also laevosan and hetastarch showed no significant interaction.

Further evidence for a phycobilisome model from selective dissociation, fluorescence emission, immunoprecipitation, and electron microscopy

Phycobilisomes, isolated in 500 mM Sorensen's phosphate buffer pH 6.8 from the red alga, Porphyridium cruentum, were analyzed by selective dissociation at various phosphate concentrations. The results are consistent with a structural model consisting of an allophycocyanin core, surrounded by a hemispherical layer of R-phycocyanin, with phycoerythrin being on the periphery. Such a structure also allows maximum energy transfer. Intact phycobilisomes transfer excitation energy ultimately to a pigment with a fluorescence emission maximum at 675 nm. This pigment is presumed to be allophycocyanin in an aggregated state. Uncoupling of energy transfer among the pigments, and physical release of the phycobiliproteins from the phycobilisome follow a parallel time-course; phycoerythrin is released first, followed by R-phycocyanin, and then allophycocyanin. In 55 mM phosphate buffer, the times at which 50% of each phycobiliprotein has dissociated are: phycoerythrin 40 min, R-phycocyanin 75 min, and allophycocyanin 140 min. The proposed arrangement of phycobiliproteins within phycobilisomes is also consistent with the results from precipitation reactions with monospecific antisera on intact and dissociated phycobilisomes. Anti-phycoerythrin reacts almost immediately with intact phycobilisomes, but reactivity with anti-R-phycocyanin and anti-allophycocyanin is considerably delayed, suggesting that the antigens are not accessible until a loosening of the phycobilisome structure occurs. Reaction with anti-allophycocyanin is very slow in P. cruentum phycobilisomes, but is much more rapid in phycobilisomes of Nostoc sp. which contains 6–8 times more allophycocyanin. It is proposed that allophycocyanin is partially exposed on the base of isolated intact phycobilisomes of both algae, but that in P. cruentum there are too few accessible sites to permit a rapid formation of a precipitate with anti-allophyocyanin. Phycobilisome dissociation is inversely proportional to phosphate concentration (500 mM to 2 mM), and is essentially unaffected by protein concentration in the range used (30–200 μg/ml). Phycobiliprotein release occurs in the same order (phycoerythrin > R-phycocyanin > allophycocyanin) in the pH range 5.4–8.0.