3. (8 points) Carboxymethyl cellulose is a water-insoluble material consisting o

Question

3. (8 points) Carboxymethyl cellulose is a water-insoluble material consisting of cellulose with carboxylmethyl groups attached to it as shown to the right. Suppose a mixture of the peptides listed below was subjected to ion exchange chromatographyCellulose on a column of carboxymethyl cellulose at pH 7.5. Indicate the order in which the peptides would elute from the column by writing 1 next to the peptide that would elute first, 2 next to one that would elute second, 3 next to the one that would elute third, and 4 next to the one that would elute last. Jo Gly-Asp-Glu-lle His-Met-Phe-Val __ Trp-Asn-Lys-Ser Thr-Tyr-Glu-Gln 2

Explanation / Answer

As per the theory, the carboxymethyl cellulose acts as a cation exchange resin in a column of ion exchange chromatography. The charge of a cation exchanger in negative and it attracts positive charge molecules. We can solve this question according to the PI value of the given peptides. The PI values of the given peptides and the charge on the peptides at pH 7.5 are

1. Gly-Asp-Glu-Ile - 3.29 (charge at pH 7.5 is negative)

2. His-Met-Phe-Val - 7.37 (charge at pH 7.5 is negative)

3. Trp-Asn-Lys-Ser - 9.07 (charge at pH 7.5 is positive)

4. Thr-Tyr-Glu-Gln - 3.64 (charge at pH 7.5 is negative)

The order of the peptides according to the charge they have is 1-4-2-3 from negative to positive.

In the cation exchange chromatography, the more negative compound will elute first.

So in the above peptides, the sequence of elution will be 1-4-2-3.

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