What does b-mercaptoethanol do to secretory proteins?also...If you forgot to add b-mercaptoethanol to a secretory protein, would the protein's migration likely speed up or slow down? Why?

β-mercaptoethanol is a reducing agent commonly used in protein sample preparation for techniques such as sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. It functions by reducing disulfide bonds in proteins, thereby denaturing them and breaking their quaternary structure.

In the context of secretory proteins, which are proteins meant to be secreted out of the cell, β-mercaptoethanol has two main effects:

1. Disruption of Disulfide Bonds: Many secretory proteins contain disulfide bonds, which are important for their proper folding and stability. β-mercaptoethanol breaks these disulfide bonds, leading to the denaturation of the protein. This denaturation causes the protein to lose its folded structure and results in the exposure of hydrophobic regions that are normally buried in the interior of the protein.

2. Reduction of Protein Aggregates: In some cases, secretory proteins can form aggregates or multimers. The addition of β-mercaptoethanol can disrupt these aggregates by reducing intermolecular disulfide bonds or disulfide bridges that hold the protein complexes together. This allows the proteins to migrate as monomers during electrophoresis.

Now, let's address the second part of your question. If you forgot to add β-mercaptoethanol to a secretory protein sample, the protein's migration during electrophoresis would likely slow down. This is because β-mercaptoethanol helps denature the proteins by disrupting their disulfide bonds, causing them to lose their folded structure. Denatured proteins generally have a more extended conformation, making them easier to separate based on molecular weight during electrophoresis. Therefore, without β-mercaptoethanol, the intact disulfide bonds would keep the protein in a more compact shape, resulting in slower migration through the gel due to increased steric hindrance.

In summary, β-mercaptoethanol disrupts disulfide bonds in secretory proteins, leading to their denaturation and facilitating their separation during electrophoresis. Failure to add β-mercaptoethanol would slow down the protein's migration because intact disulfide bonds maintain the protein's folded structure, resulting in increased steric hindrance.