Why does globular protein have good solubility in saline solution prepared using water?

Answer 1

This is a tricky question because it is based on the assumption that all globular proteins do have good solubility in saline solution prepared using water. In fact, there are many proteins that form aggregates when dissolved in water that has some salt in it.

Generally speaking, though, it is true, that many globular proteins are soluble in aqueous solutions such as phosphate buffered saline at neutral pH at room temperature and a concentration that is less than 100 mg/ml. When you look at the solubility behavior of a particular protein though, it is evident that some protein species may prefer a slightly acidic pH, whereas others prefer an alkaline pH and 500 mM of NaCl salt. Otherwise they aggregate. Aggregate formation is a big pain when working in the lab with protein solutions. Ideally one would create a solubility profile first and then adjust the buffer conditions for functional assays, chromatographic purification and analysis.

Answer 2

Globular proteins have good solubility in saline solution because the charged side chains of amino acids on the protein surface interact with the ions in the solution, forming electrostatic interactions that stabilize the protein's structure and keep it dissolved. The polar nature of water also helps to disrupt hydrogen bonds between protein molecules, allowing them to remain dispersed in the solution.