Name: Michael Johnson
Partner: David Logad & Nandita
Date: 2nd 9th September 2004
Group: Thursday 11:30am - 3:30pm
In 1888 Hofmeister that it can be possible to dehydrate a protein by adding salt to the solution, salting out. When a protein in a aqueous solution it is surrounded by water, in fact there can be up to 0.35g of water tightly bound to 1g of protein (Simpson 2004).
Also the effectiveness of the salting out can be affected by the type of salt used. This is because of the charge the salt can bring on the protein making it either likely or less likely interacted with water.
"The protein structure can also have an affect with it hydophobicity with hydrophobic patches on it (caused by the side chains Phe, Tyr, Leu, Ile, Met & Val). So the optimum salt is one that will cause hydration of the polar regions and dehydration of the hydrophobic regions of the protein. With which the salt does not interact directly with the protein. The best salts have a multivalent anions like sulphate or phosphate with cations like sodium or ammonium."(Scopes, 1994)
The Ion exchanges exploit the different net charges on proteins at a given pH and interact with the proteins on electrostatic attraction (Scopes, 1994). The carboxymethycellulose (CMC) is a cation exchange that is chemical weak. It has a negative charged carboxyl groups, they are active above the pH of 4.5.
The Sodium dodcecyl sulphate (SDS) gel is based on the principle that the proteins are all given a negative charge. This allows all proteins to migrate to the positive end of the gel. The gel is made of a certain size pore which means the migrtation is based only on the size of the proteins. The smallest proteins will migrate to the positive electrode before the larger ones and the size can be determined by a marker which has a selection of known molecular weight proteins.