Recently, Asante-Appiah et al.(Asante-Appiah, E.; Seetharaman, J.; Sicheri, F.; Yang, DS-C.; Chan, WW-C. Biochemistry1997, 36, 8710–8715) reported that 2-ethyl-2-methylsuccinic acid is a highly potent inhibitor for carboxypeptidase A (CPA), a prototypic zinc protease.