At what pH will the following peptides be hard to separate by...

[ghaithl]

...electrophoresis: Lys-his-pro-asp-ala-arg-glu-phe? At what pH will the following peptides be hard to separate by electrophoresis:
Lys-his-pro-asp-ala-arg-glu-phe-ser
Lys-his-pro-asn-ala-arg-glu-phe-ser
a-4.5
b-9.0
c-2.3
d-12.3
e-6.6
and why ? explain please ?

[Kunal Pandya]

Ans is c- pH 2.3

At pH 2.3 the following peptides be hard to separate by electrophoresis:
Lys-his-pro-asp-ala-arg-glu-phe-ser
Lys-his-pro-asn-ala-arg-glu-phe-ser

Because at this pH Side chain of aspartic acid remains protonated and not contribute to generate -ve charge so both the peptide having same Net charge.

While in all other pH value peptide Lys-his-pro-asp-ala-arg-glu-phe-ser having one extra -ve charge because of aspartic side chain, SO it separated from other peptide Lys-his-pro-asn-ala-arg-glu-phe-ser as it having Asparagine which having amide side group so not contribute any extra charge at any pH.

Regards