Examination of the carboxylesterase phenotype in human liver

► Carboxylesterase (CES) phenotype in human liver was examined. ► Reporter substrates and activity-based probes were used to measure CES activity. ► Individual livers had similar levels of CES1 protein but variable CES1 activities. ► Using bioorthogonal activity probes, the half-life of CES1/2 was 96 h in HepG2 cells.