RSCLFD peptide?

Question

rsclfd peptide if at 6.3pH, what is the pI and what different pH is this peptide a good buffer?

Answer 1

This sounds like a butchered and partial homework problem. The peptide has 4 ionizable groups: alpha amino and alpha carboxyl and the ionizable sidechain groups on aspartic acid and arginine. The approximate pKa's for those for groups are 9.04, 1.88, 12.48 and 3.65, respectively. The peptide can function as a buffer in a solution with a pH that is around any of those pKa's. The isoelectric point (pI) is the pH at which the peptide has a net charge of 0. That point will be half-way between the pKa of the sidechain carboxyl group of aspartic acid and the alpha amino group of arginine, or about 6.35.