Bio-Rad GS-900™ Calibrated Densitometer - Manual (Page 25)

Vertical Electrophoresis Systems
for SDS-PAGE
The electrophoresis systems offered by Bio-Rad
for second-dimension electrophoresis are detailed
in the table.
■ ■
The Mini-PROTEAN system includes the
Mini-PROTEAN Tetra cell (with a capacity
of up to four gels) and the high-throughput
Mini-PROTEAN
® 3 Dodeca ™ cell (for running up to
12 gels). These systems accommodate 7 cm IPG
strips and are compatible with handcast or precast
Mini-PROTEAN gels (8.6 × 6.7 cm)
■ ■
The Criterion ™ system includes the Criterion
cell (for 1–2 gels) and the high-throughput
Criterion Dodeca cell (for 1–12 gels); both cells
accommodate Criterion precast gels (13.3 × 8.7 cm)
and 11 cm IPG strips
■ ■
The PROTEAN II and PROTEAN Plus Dodeca
systems accommodate 17, 18, or 24 cm IPG strips.
The PROTEAN II system provides the ability to
choose the glass plates, spacer, and sandwich
clamps to cast two gel lengths: 16 or 20 cm.
The PROTEAN Plus Dodeca cell allows maximum
throughput for 2-D electrophoresis, with the
capability to run up to 12 2-D gels at a time
PowerPac ™ Power Supplies
Power supplies are required to meet the power
requirements of numerous applications. The choice
of power supply for second-dimension PAGE usually
depends on the size and number of gels being run:
■ ■
Use the PowerPac Basic or PowerPac HC high-
current power supply for mini-format vertical
PAGE applications
■ ■
Use the PowerPac HV high-voltage or PowerPac
Universal power supply for large-format vertical
PAGE applications
■ ■
Use the PowerPac HC power supply for
applications that require high currents, such as
PAGE with the high-throughput Dodeca cells
Bio-Rad’s vertical electrophoresis systems.
Mini-PROTEAN System Criterion System PROTEAN II System PROTEAN Plus System
Cells Mini-PROTEAN Tetra Cell Criterion Cell PROTEAN II XL Cell PROTEAN Plus Dodeca Cell
Mini-PROTEAN Dodeca Cell Criterion Dodeca Cell PROTEAN II XL Multi Cell
Number of gels 1–4 1–2 1–4* 1–12
1–12 1–12 1–6
Gel formats Mini-PROTEAN precast Criterion precast PROTEAN II handcast PROTEAN Plus handcast
Mini-PROTEAN handcast Criterion empty cassettes
IPG strip length 7 cm 11 cm 17 cm 18 and 24 cm
PowerPac Basic
Power Supply
PowerPac HC High-Current
Power Supply
PowerPac HV High-Voltage
Power Supply
PowerPac Universal
Power Supply
Precast Gels for Second-Dimension
SDS-PAGE
Bio-Rad offers precast gels in two size formats and
in a variety of formulations, some of which feature
IPG wells to hold two lengths of ReadyStrip
™ IPG
strips (7 cm and 11 cm).
Bio-Rad’s TGX ™ (Tris-Glycine eXtended shelf life)
precast gels are Laemmli gels with a proprietary
modification that extends shelf life to 12 months
and allows gels to be run at higher voltages without
producing excess heat. The TGX formulation does
not require special, expensive buffers. Like Tris-HCl
gels, TGX gels use a discontinuous buffer system,
with glycinate as the trailing ion, and are, therefore,
compatible with conventional Laemmli and
Tris/glycine/SDS buffers. These are the best
choice when long shelf life is needed and
traditional Laemmli separation patterns are desired.
TGX Stain-Free
™ gels are Laemmli-like extended
shelf life gels that allow rapid fluorescent detection
of proteins with the stain-free enabled imagers
Gel Doc
™ EZ and ChemiDoc ™ MP, eliminating
staining and destaining steps. Other precast
gel formulations have also been developed to
circumvent the shelf life issues of Tris-HCl systems.
* For 2-D applications running a maximum of 2 gels at a time is recommended.
46 47
2-D Electrophoresis Guide Theory and Product Selection Chapter 4: The Second Dimension: SDS-PAGE
Choice of Gel Size
The choice of gel size depends on the same factors
determining the length of IPG strip used, namely
speed, resolution, and throughput (see the Choice of
IPG Strip Length section):
■ ■
Mini-format systems accommodate short IPG strips
(7 cm) and mini-format gels. The short separation
distance of the gels maximizes the electrical field
strength (V/cm) to yield rapid separations with
moderate resolution. Use mini gels and systems for
rapid analysis and method development
■ ■
Midi gels and midi-format systems accommodate
11 cm IPG strips and are slightly larger (both in
width and length) gels. They still offer rapid runs,
but because of the longer separation distance,
they provide better coverage than mini-format gels
■ ■
Large-format systems accommodate 17–24 cm
IPG strips and large gels and offer the maximum
resolution possible; however, large gel sizes require
longer run times
Choice of Buffer System
The pH and ionic composition of the buffer systems
used to prepare the gels and samples and to fill the
electrode reservoirs determine the power requirements
and heavily influence the separation characteristics of
a polyacrylamide gel. Different buffer systems also
vary widely in their stability.
The most common buffer system for second-
dimension SDS-PAGE is the Tris-HCl system
described by Laemmli (Laemmli 1970). The reagents
are inexpensive and readily available, and the precast
gels are also readily available in a wide variety of gel
percentages. The system is robust and highly tolerant
of high sample loads. However, Tris-HCl resolving
gels are prepared at pH 8.6–8.8; at this basic pH,
polyacrylamide slowly hydrolyzes to polyacrylic acid,
which can compromise separation. For this reason,
Tris-HCl gels have a relatively short shelf life.
In addition, the gel pH can rise to pH 9.5 during a
run, causing proteins to undergo deamination
and alkylation, thereby diminishing resolution and
complicating post-electrophoresis analysis.
To alleviate these shortcomings, a number of
alternative buffer systems have been developed.
For example, bis-Tris, Tris-acetate, and other
proprietary buffer systems (see the Precast Gels for
Second-Dimension SDS-PAGE sidebar) offer extended
shelf life as well as other separation characteristics
unique to their formulations.
High-quality precast gels are preferred for high-
throughput applications. They provide savings in time
and labor, and the precision-poured gradients result in
reproducibility among runs.