
proteins $\xrightarrow{{enzyme{\text{ }}\left( A \right)}}$ polypeptides $\xrightarrow{{enzyme{\text{ }}\left( B \right)}}$ amino acids,
are respectively
| $pH$ at Isoelectric point | |
| $(Amino acid)_I$ | $6$ |
| $(Amino acid)_{II}$ | $9.8$ |
| $(Amino acid)_{III}$ | $3.9$ |
$(Amino acid)_{II}$ is ____ ?