Enhanced field strength and resolution in gel electrophoresis upon substitution of buffer by histidine at its isoelectric point

Electroelution of proteins from bands in gel electrophoresis without gel sectioning for the purpose of protein transfer into mass spectrometry: elements of a new procedure

Electroelution of protein bands from a gel has advantages over the competitive common technique requiring gel sectioning with respect to yield, speed and the potential for computer-controlled application to multicomponent two-dimensional (2-D) gels. The electroelution design for the commercial high-performance gel electrophoresis (HPGE) apparatus represented the most advanced technique to date until the recent discontinuation of its production. The present report serves to summarize the necessary design elements for the purpose of renewing and further developing the electroelution technique. A rudimentary technique is presented by which the electroeluate is collected in a glass tube superimposed on a reversibly stained gel band and connected to an anolyte reservoir. Although the stain used is insufficiently sensitive, the technique allowed for the qualitative verification of its usefulness in the transfer of the electroeluate into mass spectrometry.

Transfer of SDS-proteins from gel electrophoretic zones into mass spectrometry, using electroelution of the band into buffer without sectioning of the gel

Five SDS-proteins, ranging in molecular weight from 14 to 66 kDa, were detected without covalent fluorescent labeling by the automated gel electrophoresis apparatus with intermittent fluorescence scanning (HPGE apparatus, LabIntelligence) during electrophoresis in barbiturate buffer in the presence of Cascade Blue. The SDS-proteins were electroeluted from the gel into 220 microl of buffer by a modification of the procedure of Gombocz and Cortez. The electroeluate was freed of SDS, ultrafiltered and subjected to MALDI-TOF mass spectrometry. The masses of the five native proteins were found to be maintained after electrophoresis and electroelution in the presence of the potential contaminants SDS, barbituric acid and Cascade Blue. The procedure of protein transfer from SDS-PAGE into mass spectrometry, without excision of bands, gel maceration and protein recovery by diffusion, therefore is shown to be suitable for the identification by mass of intact proteins derived from gel electrophoretic bands.

Preparative application of commercial automated gel electrophoresis apparatus to subcellular-sized particles: sequential isolations, fractions re-run, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, yield and purity

The analytical and preparative potential of automated gel electrophoresis apparatus with intermittent fluorescence scanning of the migration path, the HPGE-1000 apparatus (LabIntelligence, Belmont, CA) was further developed in application to subcellular-sized particles. Resolution between two rat liver microsome components in agarose (MetaPhor) gel electrophoresis was found to increase with decreasing agarose concentration to 0.04%. It was less, even in an agarose solution at that low concentration, than that in laterally aggregated 4% polyacrylamide gel. The three components of the microsomal preparation were sequentially isolated from 0.6 and 0.8% agarose gel electropherograms. One fraction when re-electrophoresed was found to exhibit the original mobility and did not give rise to the other components. Yields of each component were near-quantitative after one or two electroelution steps. Based on protein content, no impurities could be detected in two of the microsome fractions; the third fraction contained 2% of nonmicrosome impurity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of all three microsome fractions were indistinguishable from one another and from that of the unfractionated microsome preparation.

The band areas of proteins determined by fluorescent scanning in the commercial automated gel electrophoresis apparatus

An automated gel electrophoresis apparatus, recently available commercially, allows one to follow the band during electrophoresis in real time, and lends itself therefore to an evaluation of bandwidth as a function of migration time (the dispersion coefficient), resolution and band shape. These determinations assume the constancy of band area with migration time and at various gel concentrations. The purpose of the present study was to verify these assumptions. Representative proteins and sodium dodecyl sulfate (SDS)-proteins, either natively fluorescent or fluorescein carboxylate labeled, were found to exhibit band areas which approach constancy as a function of migration time in both agarose and polyacrylamide gel electrophoresis, provided that (i) the protein concentration under the band was low enough to obviate self-quenching of fluorescence; (ii) the separation of the protein of interest from contaminants had progressed sufficiently during the time at which band areas were measured; (iii) the baseline under the peak was sufficiently well defined. However, band areas decrease with increasing gel concentration. Protein peaks exhibited leading and trailing tails. The ratio of the combined tail area to total area appeared to be near-constant at varying migration times. However, that ratio increases with increasing gel concentration. The tail area does not appear to be an artifact of fluorometric detection since it is reproduced upon fluorimetric analysis of the protein eluted from gel slices after electrophoresis. However, it may be due to photochemical destruction under the conditions of repetitive fluorometric peak detection.

Enhanced detection sensitivity of "fluorescence reduction" by shifting the analyte absorbance spectrum and use of a fluorescent paper with higher signal/noise ratio

Nonfluorescing protein bands can be detected by the fluorescence optics of the commercial gel electrophoresis apparatus with automated scanning of the migration path (HPGE-1000, LabIntelligence, Belmont CA), taking advantage of the decrease of emission from a fluorescent paper placed below the gel by the absorbance of proteins ("fluorescence reduction"). That decrease of fluorescence gives rise to an inverted protein peak. Nonfluorescent colorless proteins appear to reduce the intensity of light emitted from the fluorescent paper due to absorbance of incident and emitted light. When the absorbance spectrum only slightly overlaps with the excitation and emission spectra of the fluorescent paper, that reduction is weak, and detection sensitivity in that application is consequently only 1/30 of that of fluorescent proteins. By contrast, when the protein is colored so that its absorbance spectrum overlaps widely with the excitation and emission spectra of the fluorescent paper, the sensitivity of "fluorescence reduction" equals 1/4 to 1/5 of that obtained for fluorescent proteins. Bands detected by "fluorescence reduction" provide a quantitative measure of protein load and mobility. The area of the inverted bands is proportional to protein loads up to 16 microg/lane of the gel tray. A theory of "fluorescence reduction" is presented which accounts for the existence of a linear relationship between band area and load.

The resolution between two native proteins and between their sodium dodecyl sulfate-complexes in agarose and polyacrylamide gel electrophoresis

Commercial gel electrophoresis apparatus with intermittent fluorescence scanning of the migration path (HPGE-1000 apparatus, LabIntelligence) makes it possible to measure band width and migration distance as a function of the duration of electrophoresis. As a result, resolution can be evaluated quantitatively and therefore different gel media can be compared objectively. The resolution of fluorescein carboxylate labeled conalbumin (molecular mass 86 kDa) and soybean trypsin inhibitor (22.7 kDa) in gel electrophoresis was found to increase as a function of the gel type in the order SeaKem GTG-, SeaKem Gold-agarose, 2% N,N'-methylenebisacrylamide cross-linked polyacrylamide, MetaPhor-XR-, and SeaPrep-agarose. The advantage in resolving capacity of SeaPrep agarose over the polyacrylamide gel was by a factor of up to five. The resolving capacity of the agaroses was in indirect relation to the degree of electroendosmosis. In all media, resolution increased with migration distance (time). The same proteins when reacted with sodium dodecyl sulfate (SDS) resolve (i) better at up to 6% SeaPrep agarose concentration than in polyacrylamide, as in the gel electrophoresis of the native proteins; (ii) less effectively, by contrast, at SeaPrep agarose concentrations > 6%, than in polyacrylamide gel; and (iii) significantly better in 4-6% SeaPrep agarose than in 4-6% SeaKem GTG agarose. Since Ferguson plot analysis in both agarose and polyacrylamide gels shows that the two SDS-proteins are larger than the native proteins with which they are complexed, the superiority of polyacrylamide gels above 7% appears to be correlated with the fact that its mean pore radius, estimated for both media using identical assumptions and identical rigid spherical standards - proteins, is approximately seven times larger than that of SeaPrep agarose in the concentration range of 3-8%, and that therefore the molecular "fit" in polyacrylamide is closer than that in SeaPrep agarose of the concentration range used. The dependence of resolution on the ratio of particle radius to mean pore radius ("fit") is also suggested by the fact that the two SDS-proteins resolve in a biphasic dependence on gel concentration in both agarose and polyacrylamide, with a maximum at 6% agarose and 10% polyacrylamide.

Isolation of subcellular-sized particles separated by electrophoresis in dilute polymer solution, using commercial electrophoresis apparatus with intermittent scanning of fluorescence

Resolution of subcellular-sized particles in electrophoresis employing semi-dilute polymer solutions as "sieving media" improves as the polymer concentration is decreased. Therefore, the previously reported conditions of preparative electrophoresis of microsomes, using concentrated (12%) polyvinylpyrrolidone (PVP) solutions, while solving the problem of non-entrance of large particles into "sieving media", do not provide adequate resolving capacity, as exemplified by failure of the microsome preparation used, to resolve in the manner of gels or dilute solutions. The present report provides the conditions under which the HPGE-1000 apparatus can be preparatively applied when the electrophoretic separation is effectively conducted in a dilute polymer solution. The isolation of three microsome components under those conditions constitutes the first application of "particle sieving", i.e., a separation due preponderantly to size and shape differences, at a preparative scale.

Improved resolution in the gel electrophoresis of proteins by a periodically interrupted electric field

The capability of the commercial gel electrophoresis apparatus with intermittent scanning of fluorescence (HPGE-1000, LabIntelligence) to provide time-dependent zone dispersion allows one to quantitate resolution. Using a model protein separation, that between phycoerythrin and fluorescein-labeled conalbumin, resolution was compared between separations conducted at a constant field strength of 80 V/cm and one conducted in 10-s pulses of the same field strength, interrupted periodically by 120 s in the absence of an electric field. Resolution was improved by a factor of two in the discontinuous application of the electric field compared to that obtained in its continuous application. Similarly, the intermittent application of 80 V/cm for 10 s, followed by 120-s pauses, gave rise to twice the resolution obtained from a continuous application of 7 V/cm.