Question

20.An enzyme solution was treated with a saturated ammonium sulfate. What are the consequences of such treatment in relation of this protein structure and properties?

Answer 1

Ammonium sulfate is widely employed as precipitating agent to purify enzymes/proteins. Ammonium sulfate is highly soluble salt and will dissociate into NH₄⁺ and SO₄^2- ions in aqueous solutions that are belong to Hofmeister series. These ions are readily attracted to the opposite charges present on the protein surface. As a consequence, interaction of the water molecules with protein is prevented. This leads to precipitation of enzyme from the solution. Actually, this concentration dependent process.  This process is termed as "salting out" and as it happens when concentration ammonium sulfate is increased in step-wise.

In general,ammonium sulfate does not denature the proteins. It preserves the native state of proteins. Infact, some proteins are commercially sold by storing them in ammonium sulfate. This is also due to the fact that ammonium sulfate also inhibits bacterial growth. At only very high concentrations, ammonium sulfate dehydrates few proteins thus causing denaturation.