Separation and Purification

Question 1

At pH 7, which of the following peptides will bind to an anion-exchange column and require the lowest concentration of NaCl for elution?
A peptide with an overall charge of -5, +1, -1, +5 ?

Answer 1

THe one with the overall charge of -1.

This Biochemistry question falls under the content category “Separation and purification methods.” The answer is C because the anionic peptides bind to anion-exchange columns. The strength of the binding depends on the overall charge of the peptide. Of the options given, only C and D have a net negative charge. The net charge of peptide C is –1, whereas the net charge of peptide D is –5. Peptide C would elute at a lower salt concentration than Peptide D. This is a Reasoning about the Design and Execution of Research question because you must understand the design of an anion-exchange experiment and the role of elution in that design to determine the appropriateness of a technique.