A sensitive method for the detection of beta-galactosidase in transfected mammalian cells

A sensitive method has been developed for the detection of E. coli beta-galactosidase in transfected HeLa cells. The chromogenic substrate, CPRG (chlorophenol red-beta-D-galactopyranoside), was compared with ONPG (o-nitrophenyl-beta-D-galactopyranoside) by kinetic analysis with purified beta-galactosidase. The Km for CPRG was 1.35 mM and the Vmax was 21.4, whereas the Km for ONPG was 2.42 and the Vmax was 41.1. CPRG at 8.0 mM (6-fold Km) gave 86% of the Vmax and was used as the standard concentration for quantitation of enzyme levels. The Vmax for CPRG was half that for ONPG, and chlorophenol red has an extinction coefficient that is 21-fold higher than o-nitrophenol; these factors make CPRG about 10-fold greater in sensitivity for the quantitation of enzyme levels. The use of Nonidet P-40 to lyse the cells and the use of CPRG as substrate permitted the rapid detection of low levels of enzyme production from transfected human cells that could not be detected using ONPG.