4. Protein X is an all helical protein with 100 amino acids including 2 cysteines and a pl of 7.0.
Which one of the following graphs best describes the solubility of this protein under different ammonium sulphate (salt) concentrations?

How Ammonium Sulfate Affects Protein X Solubility

Protein solubility is influenced by pH, ionic strength, and salt concentration. Protein X, a 100-amino-acid, all-helix protein with 2 cysteines, exhibits characteristic solubility behavior when exposed to different ammonium sulfate concentrations.

Factors Influencing the Solubility of Protein X

Protein X has a pI (isoelectric point) of 7.0, meaning it is uncharged at this pH. The presence of cysteine residues suggests potential for disulfide bonding, which may impact its structural stability. Understanding the effect of ammonium sulfate on its solubility is crucial for purification and stability studies.

Impact of Ammonium Sulfate on Protein X

1. Low Salt Concentration (Salting-In Phase)

At low ammonium sulfate concentrations, salt ions reduce electrostatic repulsion, stabilizing the protein in solution and enhancing solubility.

2. High Salt Concentration (Salting-Out Phase)

As the salt concentration increases beyond a critical point, ammonium sulfate competes with protein molecules for water, leading to precipitation and decreased solubility.

Correct Answer: Graph 2

Protein X follows the typical salting-in and salting-out pattern. Initially, solubility increases with rising salt concentration but then sharply declines at higher concentrations due to precipitation.

Understanding this behavior is essential for protein purification techniques like ammonium sulfate precipitation, widely used in biochemistry and molecular biology.

Key Phrase: Solubility of Protein X ammonium sulfate