Immobilized buffers for isoelectric focusing: from gradient gels to membranes

Hydrolytically stable, diaminocarboxylic acid-based membranes buffering in the pH range from 6 to 8.5 for isoelectric trapping separations

Diaminocarboxylic acid carrier ampholytes, such as L-histidine, 2,3-diaminopropionic acid, L-ornithine, and L-lysine, were reacted with glycerol-1,3-diglycidyl ether (GDGE) and poly(vinyl alcohol) (PVA) in the presence of sodium hydroxide to produce hydrolytically and mechanically stable hydrogels, supported on a PVA substrate, for use as buffering membranes in isoelectric trapping (IET) separations. The pH values of the DACAPVA membranes were determined with the help of small-molecule pI markers and proteins and were found to be in the 6 < pH < 8.5 range. The membranes were successfully used to isoelectrically trap small ampholytes, desalt ampholyte solutions in IET mode, and effect the binary separation of chicken egg white proteins.

Fundamental aspects of chiral separations by capillary electrophoresis

A review is presented that surveys the basic theory of direct separation of enantiomers by capillary electrophoretic (CE) techniques. These separations are based on the formation of diastereomeric complexes between the enantiomeric analytes and a chiral selector added to the electrolyte solution. The review covers a comprehensive treatment of the equations needed for optimization of selectivity coefficients, resolution and analysis time in the zone electrophoretic mode. In this context, it takes into account combined equilibria of complexation and protonation/deprotonation as well as complexation and paritition into micelles. On the basis of these equations, the benefits of charged selectors and the optimization potential inherent to pH tuning can be documented. In addition, the review deals with some basic aspects of chiral isoelectric focusing and briefly discusses indirect enantioseparation. In a subsequent section a survey is given on particularfeatures of the various types of chiral selectors. Finally, the recent developments in preparative enantioseparation in continuous free-flow system and by use of isoelectric membranes are discussed.

High-affinity LPS binding domain(s) in recombinant factor C of a horseshoe crab neutralizes LPS-induced lethality

SSCrFCES is a biologically active, recombinant fragment of factor C, which is the endotoxin-sensitive serine protease of the LAL coagulation cascade. The approximately 38 kDa protein represents the LPS binding domain of factor C. A novel secretory signal directs the secretion of SSCrFCES into the culture supernatant of Drosophila cells, and hence it is readily purified. By differential ultrafiltration followed by preparative isoelectric membrane electrophoresis, SSCrFCES was purified as an isoelectrically homogeneous and stable monomeric protein. The ability of SSCrFCES to bind lipid A was analyzed using an ELISA-based assay as well as surface plasmon resonance. SSCrFCES exhibits high positive cooperativity of binding to two or three lipid A molecules, with a Hill's coefficient of 2.2. The 50% endotoxin-neutralizing concentration of SSCrFCES against 200 EU of endotoxin is approximately 0.069 microM, suggesting that SSCrFCES is an effective inhibitor of LAL coagulation cascade. Although partially attenuated by human serum, as little as 1 microM of SSCrFCES inhibits the LPS-induced secretion of hTNF-alpha and hIL-8 by THP-1 and human peripheral blood mononuclear cells with greater potency than polymyxin B. SSCrFCES is noncytotoxic, with a clearance rate of 4.7 ml/min. The L.D.(90) of SSCrFCES for LPS lethality is achieved at 2 microM. These results demonstrate the endotoxin-neutralizing capability of SSCrFCES in vitro and in vivo and its potential use for the treatment of endotoxin-induced septic shock.

Purification of glycopeptide antibiotics by isoelectric focusing in multicompartment electrolyzers with immobiline membranes

The purification of small glycopeptides (a Hepta-Tyr of the teicoplanin family, exhibiting broad activity against highly glycopeptide-resistant enterococci) by isoelectric focusing in multicompartment electrolyzers with buffering, isoelectric membranes, is described. The main obstacle to such a preparative technique, in common with all focusing methodologies, is the poor solubility of the analyte at the pI value with resultant precipitation and coprecipitation of all impurities with the main fraction. A good solubilizing power was obtained in hydro-organic solvents, particularly a mixture of 6 M urea and 20-25% trifluoroethanol. Best results, however, were obtained with mixtures of 8 M urea and zwitterionic detergents, notably the 3-[(3-cholamidopropyl)dimethylammonia]-1-propanesulfonate (CHAPS) family. A unique behavior of the peptide was found in concentration gradients of CHAPS: solubility increases up to 3.5% CHAPS, but the curve shows a maximum and then solubility decreases again at 5% CHAPS. In mixtures of 8 M urea and 3.5% CHAPS, sample loads of 500 up to 1000 mg Hepta-Tyr could be purified in a single run, with recoveries > 90% and purity in excess of 99%. The main glycopeptide fraction (pI 8.56) was collected into an isoelectric trap delimited by pI 8.46 and pI 8.65 membranes. Attempts at purifying the glycopeptide by most known reversed phase-high performance liquid chromatography (RP-HPLC) techniques failed completely.

Immobilized pH gradients: new pK values of acrylamido buffers in poly(N-acryloylaminoethoxyethanol) matrices

A novel matrix consisting of N-acryloylaminoethoxyethanol, a hydrophilic monomer extremely resistant to hydrolysis, was recently reported by Chiari et al. (Electrophoresis, 1994, 15, 177-186). When using it as a matrix for grafting immobilized pH gradients for isoelectric focusing, a shift in protein spot position was noticed. This was attributed to a shift in pK values of the Immobiline buffers when changing from the standard poly(acrylamide) to a poly(N-acryloylaminoethoxyethanol) matrix. A series of 1 pH unit gradients was constructed, where a single buffering Immobiline was used and titrated with a counterion having a pK removed by at least 3 pH units from the nearest extreme of the generated pH interval. It was noted that all compounds became weaker acids and bases, with a delta pK ranging from -0.02 to -0.06 for the acids (pK 3.6, 4.4, and 4.6) and a delta pK ranging from -0.12 tp -0.20 for the bases. The new pK values for the seven commercially available buffers are thus pK 3.6-->pK 3.58, pK 4.4-->pK 4.36, pK 4.51-->4.45, pK 6.21-->6.09, pK 7.06-->6.94, pK 8.50-->pK 8.37, and pK 9.59-->pK 9.39. These values refer to 10 degrees C in the gel phase, the first value in poly(acrylamide) and the second in poly(N-acryloylaminoethoxyethanol).