Polyethylene glycols of various molecular weights and high-ionic strength salts such as ammonium sulfate and sodium citrate that induce protein precipitation when used in high concentrations are classified as precipitants, while certain other salts such as zinc sulfate or calcium sulfate that may cause a protein to precipitate vigorously even when used in small amounts are considered adjutants.
Various species such as Ca2+ and Zn2+ are a biological requirement for certain proteins to fold correctly[2] and certain co-factors are needed to maintain a well defined conformation.
[5] The size of the protein-detergent mixed micelles are affected by both additives and detergents which will strongly influence the crystals obtained.
By reducing the size of the mixed micelles lattice forming protein-protein contacts are encouraged.
[6] Temperature, salts, detergents, various additives are used in this system to tailor the cubic phase to suit the target protein.