Dialysis of Proteins

Theory

Dialysis is an alternative time-consuming but efficient alternative method for concentrating proteins and remove contaminating salts and small particles like urea from eluted proteins in preparation for a downstream process.

The process works by ensuring a concentration gradient with respect to your protein sample which is held in a semi-permeable membrane which allows exchange of molecules below a certain molecular weight given by Daltons (Da). The protein sample is placed within the tubing leaving sufficient room for expansion and the ends of the tubing closed by tying a know or using clips. The sample is then submerged into a solution whose composition varies greatly depending on what you wish to get rid of and by how much for example if I wanted to get rid of all the urea in my samples then in my outside solution I would have no urea in it. A concentration gradient is established and urea in the sample will diffuse through the membrane into the surrounding solution in order to achieve equilibrium. The amount of reduction is related to the volume of the surrounding solution and composition

Practice

In practice the exact procedure for dialysis varies hugely depending on the desired levels of purity vs sample loss

Preparation of Dialysis Tubing

Membrane Dialysis

Microcentrifuge Dialysis

Health and Safety

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