2.B.110.  The pH-dependent Enzyme-responsive ProCarrier (ErPC) Family 

Kyu-Sung Jeong and co-workers reported enzyme-responsive procarriers 43a–d having pendant hydrophilic groups (see figure below) (Choi et al. 2016). The hydrophilic groups prevent membrane insertion. Enzyme-mediated hydrolysis of the hydrophilic appendage in situ enables membrane permeation and chloride transport (Fig. 28b). The enzyme activity is pH dependent. Procarrier 43a is hydrolyzed by porcine liver esterase at pH 7.4, while 43d is hydrolyzed by Aspergillus oryzae β-galactosidase at pH 5.5. Given the substrate- and enzyme-coupled pH dependence, the ion transport activity can be carefully tuned in these systems.