Protein Gel Electrophoresis Chamber Systems

Invitrogen electrophoresis chamber systems are tanks composed of an upper (anode) and lower (cathode) buffer chamber connected by platinum wire electrodes. Gels are held vertically between the buffer chambers during electrophoresis. Applying an electrical field across the buffer chambers forces the migration of proteins into and through the polyacrylamide gel. When current is applied, the smaller molecules migrate more rapidly and the larger molecules migrate more slowly through the gel matrix.

Resistance

The electrical resistance of the assembled electrophoresis cell is dependent on buffer conductivity, gel thickness, temperature, and the number of gels being run. Although the resistance is determined by the gel system, the resistance varies over the course of the run.

• In discontinuous buffer systems (and to a lesser extent in continuous buffer systems) resistance increases over the course of electrophoresis. This occurs in the Tris-glycine buffer system as highly conductive chloride ions in the gel are replaced by less conductive glycine ions from the running buffer.
• Resistance decreases as the temperature increases.

Voltage

The velocity of an ion in an electric field varies in proportion to the field strength (volts per unit distance). The higher the voltage, the faster an ion moves. For most applications, we recommend a constant voltage setting.

• A constant voltage setting allows the current and power to decrease over the course of electrophoresis, providing a safety margin in case of a break in the system.
• The constant voltage setting does not need adjustment to account for differences in number or thickness of gels being electrophoresed.

Current

For a given gel/buffer system, at a given temperature, current varies in proportion to the field strength (voltage) and cross-sectional area (thickness and number of gels). When using a constant current setting, migration starts slow, and accelerates over time, thus favoring stacking in discontinuous gels. When running under constant current, set a voltage limit on the power supply at, or slightly above the maximum expected voltage to avoid unsafe conditions. At constant current, voltage increases as resistance increases. If a local fault condition occurs (e.g., a bad connection), high local resistance may cause the voltage to reach the maximum for the power supply, leading to overheating and damage of the electrophoresis cell.

Power

Wattage measures the rate of energy conversion, which is manifested as heat generated by the system. Using constant power ensures that the total amount of heat generated by the system remains constant throughout the run but results in variable mobility since voltage increases and current decreases over the course of the run. Constant power is typically used when using IEF strips. When using constant power, set the voltage limit slightly above the maximum expected for the run. High local resistance can cause a large amount of heat to be generated over a small distance, damaging the electrophoresis cell and gels.