The single-reagent-addition, homogeneous, fluorescent assay measures cell viability and cytotoxicity by detecting two distinct protease activities. The live-cell protease activity is restricted to intact viable cells and is measured using a fluorogenic, cell-permeant peptide substrate (GF-AFC Substrate). The substrate enters intact cells where it is cleaved to generate a fluorescent signal proportional to the number of living cells. This live-cell protease activity marker becomes inactive upon loss of membrane integrity and leakage into the surrounding culture medium. A second, cell-impermeant, fluorogenic peptide substrate (bis-AAF-R110 substrate) is used to measure dead-cell protease activity that has been released from cells that have lost membrane integrity.
The homogeneous, "add-mix-measure" protocol eliminates parallel plate processing and reduces cell culture costs, and the ratio of live:dead cells is independent of cell number and normalizes data. Data normalization for cell number makes results more comparable well-to-well, plate-to-plate, day-to-day.
Complementary live- and dead-cell measures with independent chemistries serve as internal controls for each other, and multiplexing capability with most Promega bioluminescent cell-based apoptosis or genetic reporter assays results in more data per well.