关于氨基酸pI特征的描述,一般书上均为:(1)净电荷为零;(2)主要以两性离子存在。我认为第(2)点如改用“两性离子达极大值,”则更能反映 pI 的特征。因“主要以两性离子存在”。不仅在 pI 时如此,实际上在 pH 大于pK_1~′,小于 pK_2~′的范围内都如此。而极大值则只在 pI 这一点上才达到。此外,有些学生往往误解:在 pI 时主要以两性离子存在,则不在 pI 时就主要不以两性离子存在。例如向学生提这样 A description of the amino acid pI characteristics, the general book are: (1) net charge is zero; (2) mainly zwitterions exist. I think the point (2), such as the switch to “zwitterions up to the maximum,” is more able to reflect the characteristics of pI. Because of “the main existence of zwitterions.” This is true not only at pI, but actually at pH values ​​above pK_1 ~ ’and below pK_2 ~’. The maximum is only achieved at pI. In addition, some students often misunderstood: the main zwitterion in the pI exists, then not in pI when the main does not exist as zwitterions. For example, to mention this to students