Do I need to boil the samples before loading in non-reducing SDS-PAGE? What are the electrophoresis conditions for non-reducing bands when looking at intramolecular disulfide bonds of a 25kDa protein?

Whether to boil the sample in a non-reducing SDS-PAGE experiment depends on your experimental purpose and the characteristics of the protein.

 

I. Should you boil the sample before loading on non-reducing SDS-PAGE?

1. You may choose to boil or not boil, but do not add DTT/β-ME.

2. Slight heating at 50°C for 5 minutes can aid denaturation, while not boiling the sample can help maintain the protein closer to its native conformation.

 

II. Electrophoresis conditions for detecting intramolecular disulfide bonds in a 25 kDa protein

1. Sample buffer (without reducing agent): SDS 2%, Tris-HCl (pH 6.8) 62.5 mM, glycerol 10%, bromophenol blue 0.01%.

2. Gel: separating gel 12-15%, stacking gel 4-5%.

3. Electrophoresis buffer (without DTT/β-ME): Tris 25 mM, glycine 192 mM, SDS 0.1%.

4. Electrophoresis conditions:

(1) Constant voltage of 80V (stacking gel) → 120V (separating gel).

(2) Or constant current of 20-30 mA.

 

III. Expected results

1. With intramolecular disulfide bonds: higher mobility under non-reducing conditions (faster migration).

2. No impact from disulfide bonds: no significant difference in band position.

It is recommended to run both reducing and non-reducing SDS-PAGE for comparison.

 

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