BL/CH 401 Lecture 6

Protein/Enzyme Purification -- PART I

Section B

Separation of Proteins by Difference in Surface Charge

Imagine the protein as a sphere with charged AA side chains on its surface

{*Figure 2*}

By summing the surface charges the net charge of the protein at a set pH, the protein will have negative, neutral, or positive charge. This is related to the pI of the protein.

The method of ion exchange chromatography can be used to separate proteins with differing charges.

Usually, the fixed charge groups are attached to cellulose fibers or beads. Shown here is one cellulose fiber with protein bound to charged group on cellulose particle:

Figure 3. Anion Exchanger (Protein with Negative charge)
Example: DEAE Cellulose (Solid support with Positive Charge groups)

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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu

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