Separation and isolation of subcellular-sized particles by electrophoresis in polymer solution using the commercial scanning apparatus

Electrokinetic transport and separations in fluidic nanochannels

This article presents a summary of theory, experimental studies, and results for the electrokinetic transport in small fluidic nanochannels. The main focus is on the effect of the electric double layer on the EOF, electric current, and electrophoresis of charged analytes. The double layer thickness can be of the same order as the width of the nanochannels, which has an impact on the transport by shaping the fluid velocity profile, local distributions of the electrolytes, and charged analytes. Our theoretical consideration is limited to continuum analysis where the equations of classical hydrodynamics and electrodynamics still apply. We show that small channels may lead to qualitatively new effects like selective ionic transport based on charge number as well as different modes for molecular separation. These new possibilities together with the rapid development of nanofabrication capabilities lead to an extensive experimental effort to utilize nanochannels for a variety of applications, which are also discussed and analyzed in this review.

Mass spectrometric analysis of the electroeluates of fluorescent proteins after preparative electrophoresis in the automated HPGE-1000 apparatus

Bands of green fluorescent protein (GFP) and R-phycoerythrin (PHYCO) in gel electrophoresis on the automated apparatus for gel electrophoresis with periodic fluorescence scanning (HPGE), the HPGE-1000 apparatus, were retrieved from the gel by electroelution. While PHYCO was recovered in a single volume of electroeluate buffer after the predicted migration time, GFP fluorescence was lost under the same conditions and could only be recovered using multiple changes of electroeluate buffer. The multiple volumes of buffer necessitated pooling, concentration, and storage, conditions under which a minor GFP component, GFP-II, formed artifactually. PHYCO after electroelution also exhibits a minor component present in the original preparation. The electroeluate of GFP, transferred into a mass spectrometer after pooling, concentration and storage, is indistinguishable in mass from the original preparation.

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.

Preparative electrophoresis in "sieving media" of subcellular-sized particles

The commercial gel electrophoresis apparatus with intermittent scanning of the migration path and preparative capacity (HPGE-1000, LabIntelligence) is applicable to polymer solutions as well as gels. Unresolved rat liver microsomes can be isolated from 11-15% polyvinylpyrrolidone (PVP) solution by means of a syringe. The automated band isolation technique applied under resolving conditions in dilute polymer solutions allowed for the sequential isolation of three microsome components with 85, 76 and 75% recovery, respectively, under strict control of the dimensions of the volumetric collection module of the HPGE-1000 apparatus. Separations of unlabeled microsomes and sea urchin egg components in dilute polymer solutions have been performed, using detection by "fluorescence reduction". The unlabeled major component of a sea urchin egg homogenate has been isolated from electrophoresis in 1.5% PVP (Mr = 10(6)) solution in 25-50% yield (0.24-4 microg/8 lanes of the HPGE-1000 apparatus). However, since separations of both microsomes and sea urchin egg granules in dilute polymer solutions are restricted to a narrow range of polymer concentrations, their retardation coefficients, KR = d(log mobility)/d(polymer concentration), are not ascertained.

Separation and microgram-scale isolation of sea urchin egg granules by electrophoresis in polyvinylpyrrolidone solution, using horizontal gel electrophoresis apparatus with fluorescence detector

A homogenate of sea urchin (Lytechinus pictus) eggs rich in exocytotic membrane vesicles (granules) was subjected to analytical and preparative electrophoresis in the commercial automated horizontal gel electrophoresis apparatus (HPGE-1000, LabIntelligence, Belmont, CA) capable of intermittent scanning of the migration path, using buffered solutions of polyvinylpyrrolidone (PVP). The nonfluorescent granules were detected by "fluorescence reduction", i.e., a decrease of fluorescence intensity due to the absorbance and/or light scattering properties of the particle. Granules migrated at linear migration rates in buffers ranging from 0 to 2.5% PVP. Two bands were observed and optimally separated in 1.5% PVP solution. As shown by sodium dodecyl sulfate (SDS)-polypeptide patterns, the material recovered from the bands was qualitatively indistinguishable from the two major fractions A and C of granules previously separated by free-flow electrophoresis in the absence of polymer. Ferguson plot analysis failed to provide the sizes of the granules in view of the narrow PVP concentration range available for mobility measurement and the unavailability of chemically homogeneous size standards.

High-resolution density gradient electrophoresis of proteins and subcellular organelles

Following a concept developed by Bier et al. (Electrophoresis 1993, 14, 1011-1018), binary mixtures of amphoteric buffers with low conductivity and a good buffering capacity permit rapid rate zonal separation of proteins on a density gradient electrophoresis apparatus (7 cm, x 2.2 cm). At pH 8.66 and 250 V, beta-lactoglobulin (Mr 36600) was separated into the A and B isoforms within 44 min; human transferrin (Mr 76000-81000) was separated into its sialylated glycoforms and carbonic anhydrase (Mr 30000) separated into its isoenzymes. From these results we arrive at the term high-performance density gradient electrophoresis. Compartments belonging to the endosomal system were separated by density gradient electrophoresis. Early endosomes, recycling vesicles, intermediate endosomes, late endosomes and lysomes became well-separated after 80 min at 10 mA using [125I]transferrin and horseradish peroxidase as reporter molecules in pulse-chase regimes. Mixtures of Bier buffers and standard electrophoresis media permitted very short separation times (19 min at 10 mA) for the endosomal compartments. Concommittantly, endoplasmic reticulum and proteasomes were well resolved.

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.

Preparative electrophoresis in a concentrated polymer solution: automated procedure for microsome isolation

A recently introduced automated gel electrophoresis apparatus with an intermittent scanning of the migration path, the HPGE 1000 apparatus (LabIntelligence, Belmont, CA) has a unique preparative feature: A recovery cup can be automatically positioned on the band of interest, which is then electroeluted with fluorescence monitoring of recovery. Electroelution time is extended stepwise until quantitative recovery is attained. This preparative procedure has been extended from electrophoresis in gels to that of subcellularsized particles in concentrated polymer solutions Chang et al., Electrophoresis 17, 776-780, 1996). However, that application required manual rather than computer-directed positioning of the recovery chamber over the band. The present report details a modification of instrumentation and procedure by which automated operation was restored. The modified procedure extends the benefits of automation and known quantitative recovery to isolation of particles too large to enter into gels.