Consider the net charge and isoelectric point of an amino acid with ionizable side (R-) group.
(a) Identify the acidic amino acid(s) capable of having a negatively charged carboxyl side group.
(b) Identify the basic amino acid(s) capable of having a positively charged amino side group.
(c) For an amino acid with a side (R-) chain that can ionize to a negative charge, derive a general expression in terms of measured pH and known pK_a values of a-carboxyl (pK^c_a), a-amino (pK^a_a), and side group (pK^R_a), respectively, for the net charge of the amino acid.
(d) For an amino acid with a side (R-) chain that can ionize to a positive charge, derive a general expression in terms of measured pH and known pK_a values of a-carboxyl (pK^c_a), a-amino (pK^a_a), and side group (pK^R_a), respectively, for the net charge of the amino acid.
(e) Determine the isoelectric point of aspartic acid (the pH at which the net charge is zero) using the result in part (c) and pK values obtained from a reference book.