Final answer:
Proteins precipitate at high salt concentrations because the salt ions compete with the proteins for water molecules, leading to reduced protein solubility and increased protein-protein interactions, a phenomenon known as salting-out. Various salts can precipitate different proteins at distinct concentrations, and this is utilized in biochemical methods to separate or identify proteins.
Step-by-step explanation:
Proteins precipitate at high salt concentrations due to phenomena collectively known as salting-out. At low salt concentrations, a process called salting-in can occur, where small amounts of salt increase the solubility of proteins in water by enhancing protein-water interactions. As more salt is added, the ions from the salt begin to associate more with water molecules, disrupting protein-water interactions and promoting protein-protein interactions, leading to precipitation. Different proteins have varying responses to salting-out depending on the type of salt used and its concentration. Certain techniques, such as Ouchterlony assays, rely on the precipitation of proteins to visualize the formation of antigen-antibody complexes in a gel. Heating can also cause protein aggregation due to exposure of hydrophobic groups when protein structures unfold. Isoelectric pH is another factor that affects protein solubility; proteins are least soluble at their isoelectric pH and can precipitate.