Question

Some proteins are located in the periplasmic space of Escherichia coli (the compartment between the cell wall and the outer membrane). A technique known as osmotic shock selectively releases these proteins while leaving the cells otherwise intact. Why is this technique an advantage when you are interested in purifying proteins initially located in the periplasmic space?

Answer 1

Osmotic shock falls under the Non mechanical methods of cell disruption or removal of periplasmic proteins.

The periplasmic space is between the inner cytoplasmic membrane and the bacterial outer membrane. This space occupies low volume as compared to that of the whole cell.

Using mechanical methods to remove the periplasmic proteins would require large amount of heat for cooling. Enzymatic methods may affect other proteins present in the cells.

Hence, osmotic shock which includes sudden change in the concentration of the culture allows for the removal of the periplasmic proteins without damaging the integrity of the cell.

By first inserting the cell in a hypotonic solution, water goes inside the cell and then introducing a hypertonic solution, the water along with the proteins comes out of the cell.