Stabilization of pH gradients in buffer electrofocusing on polyacrylamide gel

Dynamics of gel isoelectric focusing with ampholytic dyes monitored by camera in real-time

The dynamics of gel isoelectric focusing were studied by using amphoteric low-molecular-mass colored substances (isoelectric point markers). The polyacrylamide gel in slab format was in direct contact with the electrodes. In addition to isoelectric focusing with a pH gradient composed of synthetic carrier ampholytes, pH gradients created by simple buffers of acetic acid, 2-(N-morpholino)ethanesulfonic acid, histidine and N,N,N',N'-tetramethylethylenediamine were applied. The progress of the electrofocusing process was monitored by a charge-coupled device camera and video recording. The gradient profile and dynamics were approximated from the positions of isoelectric point markers, which were focused both on boundaries between individual zones of simple buffers and within the zones themselves. The obtained animated records enabled the observation of the entire real focusing run within fractions of a minute, which is useful both for the understanding and optimization of the focusing.

Continuous concentration of bacteria in a microfluidic flow cell using electrokinetic techniques

A novel method for the concentration of bacterial solutions is presented that implements electrokinetic techniques, zone electrophoresis (ZE) and isoelectric focusing (IEF), in a microfluidic device. The method requires low power (< 3e-5 W) and can be performed continuously on a flowing stream. The device consists of two palladium electrodes held in a flow cell constructed from layers of polymeric film held together by a pressure-sensitive adhesive. Both ZE and IEF are performed with carrier-free solutions in devices in which the electrodes are in intimate contact with the sample fluid. IEF experiments were performed using natural pH gradients; no carrier ampholyte solution was required. Experiments performed in buffer alone resulted in significant electroosmotic flow. Pretreatment of the sample chamber with bleach followed by a concentrated solution of cationic detergent effectively suppressed electroosmotic flow.

Computer applications in analysis, mapping and cataloging of proteins separated by two dimensional electrophoresis

Two dimensional electrophoretic separation of complex mixtures of proteins can only be exploited to its fullest potential using sophisticated computerized spot detection, quantification, pattern recognition, pattern normalization, data reduction and data storage. We present a discussion of some of the technical problems and of the options available which will ultimately lead toward full computerization of the data.

New polyacrylamide matrices for drift-free isoelectric focusing

The major cause for pH gradient decay and cathodic drift during isoelectric focusing in polyacrylamide gels has been found to be electroendo-osmotic flow generated by fixed charges in the gel matrix. These changes have the following causes: (a) trace impurities of acrylic acid in the co-monomers; (b) covalent incorporation of catalysts (persulphate and riboflavin 5'-phosphate) as terminal groups in polyacrylamide chains; (c) hydrolysis of amide groups to acrylic acid in the gel layer underneath the cathodic filter paper strip. The result of these fixed negative charges in the matrix is a movement of counter-ions with hydration water towards the cathode (i.e. electroendo-osmosis) with concomitant drift of pH gradient and focused protein zones in the same direction. It is impossible to cure the cathodic drift by increasing the pH of the anolyte, or decreasing the pH of the catholyte, or both, as previously suggested. One way to reduce the cathodic drift efficiently is to incorporate covalently in the matrix tertiary or quaternary groups (3-dimethylaminopropylmethacrylamide) in stoichiometric amounts as compared with the negative charges. This 'balanced' polyacrylamide displays zero drift for at least 5000 V.h, which is considered to be an ample time for equilibrium separation of protein species in isoelectric focusing.

Isoelectric focusing of immunoglobulins: improved methodology

Conditions for isoelectric focusing and detecting antibodies in thin layers of polyacrylamide have been evaluated and several improvements have been made. First, we have developed a simple method for covalently attaching the polyacrylamide gel to the glass support which improves the mechanical stability of the gel and removes the need for protein subbed plates. This in turn leads to decreased electroendosmosis and decreased background protein staining. Secondly, we have applied the methods of Nguyen and Chrambach (1977 a,b), in which amino acid solutions are used as electrodes, to focus immunoglobulins. This has eliminated cathodic drift and resulted in extremely stable pH gradients. Finally, we have found that conventional methods for detecting focused antibodies that rely on protein cross-linking before exposure to antigen often lead to distortion of the focusing patterns. Both glutaraldehyde and suberimidate destroy the antigen binding capacity of some antibodies at concentrations too low for complete fixation of protein bands. These fixation artifacts are avoided if salt-precipitated antibodies are exposed to radiolabeled antigen before fixation.

Multiple molecular forms of certain lysosomal enzymes separated by isoelectric focusing on cellulose acetate membranes

Analytical isoelectric focusing on cellulose acetate membranes offers greater resolution of the enzyme pattern than does standard electrophoresis and offers numerous advantages over other support media in isoelectric focusing. A series of lysosomal enzymes, deficiencies of which cause lethal storage diseases in infants and children, can be shown to exist as multiple molecular forms by analytical isoelectrical focusing on cellulose acetate membranes. This analytical technique should be a valuable tool in the investigation of enzyme polymorphism and genetically determined enzyme deficiency diseases.