Question

The isoelectric point (pI) of a peptide is the pH at which the peptide does not migrate in an electric field. Since the peptide is zwitterionic, there are the same number of positive charges as negative charges on the peptide population. The pI can be estimated fairly accurately (within 0.1 or 0.2 pH units) from the pK values of all the proton dissociable groups in the peptide. Using pK values from the table at the right, estimate the pI value of the following hexapeptide:

The isoelectric point (pl) of a peptide is the pH at which the peptide does not migrate in an electric field. Since the peptide is zwitterionic, there are the same number of postive charges as negative charges on the peptide population. The pl can be estimated fairly accurately (within 0.1 or 0.2 pH units) from the pK values of all the proton dissociable groups in the peptide. Using pK values from the table at the right, estimate the pl value of the following hexapeptide: Amino Acid Side Chain pK Arg 12.5 Asp 3.7 Cys 8.2 Glu 4.3 Gly-His-Glu-Lys-Phe-Cys His 6.0 Number Lys 10.5 Тyr 10.5 pl "peptide- NH3 8.0 "peptide- СООН 3.4 *Amino and carboxy terminal values differ from the a amino and carboxy values of a single amino acid

Answer 1

Antwer Phe -Ls- Atp- Cs-Thr -Tr PE-3.7 OH Ph H N OH H Pro- 3-4 NH (CH)4 SH Pra- 8.0 NH2 P=8-2 OH Ple=10. PKa-lo- Sucture will be the At PH Ph N. t HN SH OH EHN charge Over all net pho tence pI fut greater than P"+ Pro just betow pt 2- 8.OT3-7 2- 5-85